Zed Head

Check the ground from the module itself to the distributor body and from the distributor body to the engine ground. The ignition module needs a good solid ground so that it can pass the current needed to charge the coil. Most distributors have their own ground wire terminal, not sure if the ZX's did. A black wire from ground to distributor body. You don't need the ballast resistor but with that coil you should get better than you got with points. You could also have problems inside the distributor. They are known to break their stator magnets, and/or have the shaft bushing go bad causing air gap problems.

Don't take it apart if you find out it's bad and don't want to fix it yourself. I wonder if @Zs-ondabrain is still out there somewhere.

Ouch. The key to getting the drive (propeller) shaft nuts off is to have a nice little wrench (12 point is good) that will fit a nut and butt up against the body while you use a long lever (screw driver) in the u-joint to turn the shaft. Fit the wrench on the nut, with the wrench wedged against the body, then turn the shaft itself to break the nut loose. Once it's free you can usually turn it by hand.

same colors?

You'll want to check the flatness and quality of the surface on the head. Maybe have both surfaces skimmed. There's another Datsun site out there with a couple of guys that say they don't use any gasket at all. They just mill both surfaces and bolt it up. They say it works but who knows. Anyway, the head surface is often overlooked.

What was the particulate matter made of? Blowing out the 280Z high pressure fuel filters is a quick emergency fix. But replacing them with new is the right way. They have a pleated element inside that isn't going to clean up by using backward flowing air. There is one main supply line from the tank. I'd get underneath and inspect it to see if it's damaged. If it's not, maybe just buy a new filter and run it. They're cheap and your local parts store might have them. https://www.oreillyauto.com/shop/b/fuel---emissions-16775/carburetors---parts-16801/fuel-filter-water-separator-12305/6bf814fc80d2?q=fuel+filter https://www.rockauto.com/en/catalog/nissan,1975,280z,2.8l+l6,1209204,fuel+&+air,fuel+filter,6200

Removing a broken stud from the exhaust manifold is one of the hardest jobs I've done, even with it out, locked down for torquing on, and massive heat. Splitting the nut after you get room might be the best option to avoid future pain, since you're removing the engine anyway. Or just cutting the pipe in a good spot for welding on a new system. Especially if the flange isn't leaking. Those flanges can be difficult to get sealed sometimes.

Many things will be exposed when the engine is out that would otherwise be hard to get to. Something to consider. Steering rack, brake lines, fuel and vent lines, wiring stuff, clutch hoses, speedo cable, yadayada...

I think those are intentional. They raise the pressure, force per unit area, on the gasket to give a better seal.

A locksmith might be able to cut a new key that always finds the spot.

Your system might be incomplete.

SteveJ will get you where you want to be but there are some things in that document I posted that might be important. Apparently, not all 73"s are guaranteed to be the same.

Woman talks to ex on phone while new boyfriend practices guitar... Produced version.

Your emphatic "nopes" don't encourage further help. Which Vancouver are you in? These guys fixed my wiper motor. http://www.philbingroup.com/philbin_rebuilt.htm

Remove this cover. You''ll probably see the wires.

I think that Leno just likes being in the limelight. That's why he unretired. The Evans product is a product. It's for sale. They have to sell to keep the business alive. Always keep that in mind when you're looking at the claims. Here's the rationale behind the 10% MPG improvement. Reduced alternator load. https://www.greencarreports.com/news/1071361_waterless-coolant-improves-engine-life-boosts-mpg-10-percent I just watched the video again and Leno says that he really doesn't know much about cooling systems and he only runs the Evans in one of his cars. He owns 159. I watched a little more and realized that he doesn't maintain his own cars. He has people that do that for him. He's a guy with money that likes owning cars. Sorry, no offence intended. I don't see any sign that he really knows much about how engines function, let alone cooling systems. His rationale behind the corrosion of the aluminum plate on his Duesenberg is simplistic. He also said he didn't use the Evans on the Duesenberg because the "higher boiling point could affect the metal". Nonsensical. It's at 40 seconds in the video. Again, sorry to pick on Leno. He might be a successful comedian but he's not anywhere close to an expert mechanic. He has people for that. Here is an example of the depth of his advice on buying a used car. https://www.cnbc.com/2019/09/10/jay-leno-do-these-3-things-before-buying-a-used-car.html

And, any typical antifreeze has corrosion inhibitors. The Evans system always seemed like an expensive last resort to me. For the racers with overheating problems. https://prestone.com/ There have been some interesting discussions over on Hybridz about it. TimZ has a high horsepower engine and uses it. Put these words in Google - site:hybridz.org evans timz

Jay Leno is just a rich guy with expensive toys. No reason to think he's a car expert. The youtube video is an Evans advertisement. Jay probably got paid. This part in the youtube description is a big BS flag - "increases your fuel economy up to 10%,"

Meter. Test light. What you need might be in this document.

They get power depending on where the switch is, I think. There's slow, and fast, and park. Find the pin on the motor that matches the B wire and that would be your ground. Ground that pin and apply power to the other pins and something might happen. I'd work through the diagram and description and pick a pin but that would be work and it's Saturday.

You should see power at the plug. Any chance you disconnected the intermittent amp? That's what controls the power. I think it's in that area where you were doing all of your relay work.

$41,750 for a 73. https://bringatrailer.com/listing/1973-datsun-240z-171

CanTech Z uploaded this 1970 FSM to the site a while ago, it describes the F4W71A. For whatever reason the 1971 FSM is oddly formatted but it has a chapter also. The 1971 document has the same description as 1970, so it looks to be the same transmission. The 1970 document is a clearer copy. https://www.classiczcars.com/files/category/11-240z/