Zed Head

Check valve lash. It's the first procedure in the tuneup chapter.

Use heat. Makes a huge difference.

Too many possibilities. I'd get one running first and see how you like what's there. There's a ton on the internet about heads and cams and carbs and stuff.

I think it depends on which heads are on the L26, for power estimates. The stroke is longer, bore the same, but, apparently, the L26 was developed as an emissions engine, in the beginning. Usually there's "no replacement for displacement", so, with the same parts the L26 should make more power. Choices are really about the goal. Lots of possibilities.

Good find. I assume that you meant the electrodes in the cap, not points. The moisture is probably what killed the spark.

Just posting for thought. The surfaces.

Should be interesting. When I had a 1985 71C from a 300ZX I thought that it had a good balanced spread between gears. Never got to try it though, https://spicerparts.com/calculators/transmission-ratio-rpm-calculator

Just like the coolant sensor. You have to get the numbers at the ECU plug. The ECU determines how long the injectors stay open. They do that based on what's coming in through the connection to the harness. You're on the very well-worn path of people new to the Datsun EFI. Trying one thing at a time. By the end you'll have measured all of the things you need to measure, just in two weeks time instead of two hours. No offense, it is very common. Your symptoms are also what happens when the ECU goes bad, or the connector gets loose. People have fixed it, temporarily, by banging on the side of the ECU. If you had all of the test results and they were in spec. then replacing the ECU would be the last resort.

It's just a 240Z engine that's been "stroked". The first Z "stroker" engine.

How much? BAT would give you a bigger audience and probably a better price with lower fees. People seem to like it. https://bringatrailer.com/

The injectors all open at the same time. You can switch plugs at will. The throttle valve switch is a possibility. Stuck at wide open. Another piece in the meal.

Funny that you're "ticked" about the 1-2 gap but the reason people "fawn" over the close ratio units is because it gets rid of the 2-3 gap in the wide ratio transmissions. Just saying, you're making the same argument just different gears. If you think that gap is big wait until you shift in to 5th with your Case 3 gear set. Have you picked a diff ratio?

Without the actual number and knowing where it was taken, can't really tell what you're saying here. It might the the most important measurement you can make on the EFI systems. "a reading back" doesn't read well.

There's a procedure in the FSM for determining oil pump wear.

The only way to be sure that that the wires are intact from the coolant temperature sensor to the ECU is to measure resistance at the ECU plug. If you do that you are testing the wires, the sensor, and every connection along the way. I would not do anything to the coolant sensor, not even remove the plug at the sensor, until I measured resistance at the ECU plug. Start at the the end, not the middle.

"What else could it be?" is an expensive question. Better to inspect first. Did the engine ever run before it was garaged? And are you saying that no oil is being produced or no oil is squirting at high velocity? At low RPM it just dribbles.

The coolant temperature sensor is the most likely cause, based on your symptoms. You need to measure the resistance at Pin 13 of the ECU connector to ground to know for sure. Installing a new one won't help if the wires aren't connected to the ECU. I just now realized, after many years of browsing through FSM's and Fuel Injection Guides, that this drawing has the pins numbered, right in the drawing. I never looked closely enough before.

If you do install another seal make sure to put a little bit of sealant around the edges. If somebody scratched the seal mounting surface in the past (or you, maybe), you could have a leak around the outside of the seal.

I meant now. It leaks now, right? Seal quality might affect high mileage but if it's failing within 100 miles then changing to a different brand probably won't help. Maybe you damaged it during installation, of the seal or the propeller shaft. No offense, just to give you perspective, but that's a simple job. What did you use to shine up the slip yoke? It should be close to mirror finish. If you left some texture on it that might have damaged the seal. And, sometimes you just have to do things over, the same way. Might have got a defective seal.

Meet your doppelganger... https://forums.hybridz.org/topic/110792-high-rpm-shifting-dynamics/ Don't overlook the need to match the transmission ratios with the diff ratio.

Seems like it might not be the seal. There are other leak areas. Got a picture of the tail housing, with the dripping oil?

Are you sure that you have good spark? The ignition module is in the cabin with all of the humidity. Not sure what you mean by the "line" connecting the cold start valve. The CSV plugs/bolts in to a hole in the top of the manifold. Try squirting the fluid in through one of the vacuum hose holes.

What resistance value did you get? Ohms. "Checked out" might just mean you measured continuity. You need the ohms. If there's water in the fuel the filter will collect much of it. You could remove the filter and drain it in to a glass container and see if water separates out. You could also see if it starts using starter fluid. If it does that will be a clue but you'll still need to do some detective work.

Could be water in the gas, maybe. Condensation. Moist air can get in through the cap, if it doesn't seal well. Or the coolant temperature sensor isn't making good contact. You need to get resistance measurements on the coolant temperature sensor. Can't tell if you measured that or not.