Zed Head

I would check for power at the regulator plug from the main harness, and test for continuity from the regulator down to F. The circuit could be broken before, inside, or after the regulator. Looks like the switch powers the F wire and the L wire separately, in a parallel circuit. I never really looked at the circuits in detail, for the internally regulated system they just use one L wire straight to the alternator. I tried to post the FSM drawing but it failed. It's on page EE-13.

I've never had a spark plug get stuck or stripped a head thread. Seems like a solution with no problem. Anyway, many plugmakers and automakers recommend keeping the threads clean. https://ngksparkplugs.com/en/resources/5-things-you-should-know-about-spark-plugs Don't forget to adjust your torque settings down. You can strip the threads trying to avoid stripping the threads. https://www.tirereview.com/video-should-you-use-anti-seize-spark-plugs/ And make sure you pick the right one. There's a bunch. https://www.permatex.com/?s=Anti-Seize

The key to easy FPR installation is getting the hose lengths just right. Not too long. And sliding them all the way to one side before slipping the FPR in, then sliding the hose back for final fit. If that is a ZX rail and not a 78 Z rail you'll want to check cold start valve fit. The ZX's were in a different spot. Might have to do some bending.

My guess is a big bump. Poor quality heat treating on the spring steel.

They will. But the first year and a half, about, of 240Z's used a shorter shaft.

Nissan stamped letters in to the backs of their cams. You might need a mirror to see it. Here's an F cam. Some companies regrind factory cams so yours might have the Nissan stamp and the marks that siteunseen/Cliff showed. Check both ends. You can also tell by the height of the base circle. take pictures of the cam and post it.

There's a kit?

On the flywheel and plate - check that the plate cover did not get warped when you torqued it down. It's probably fine, there's some flex but if it is significant you might consider replacing to avoid chatter. On the other stuff - wealth gap increasing, billionaires taking joyrides in to space while their workers barely make it, Marx and Engels. You don't have to take a side to understand what's happening. But people should understand what's happening before they take a side. It's been studied and the things happening are not unexpected. Free market competition is one facet of a complicated picture. Winner take all just means lots of losers.

What happened to the fuel filter? Should have caught that stuff and caused low fuel pressure. If you were getting 45 psi that implies that the FPR is clogged. Better check that too. Might be hard to clean. That's a lot of crud. You can back flow the injectors with a 9 volt battery and some hoses. Good luck.

842 is on BAT, right up the way from @Racer X No reserve. I'm close too. https://bringatrailer.com/listing/1970-datsun-240z-77/

It sold. Don't know if that's a good number or not for a 510.

None of the 280Z's have replaceable propeller shaft joints. The last model to have them was the 260Z. And that was probably only the small bumper 260's.

The classic way a speed shop tries to get business. Trash the other guy or what you have so that they can sell you what they have. Beat you down then tell you that they can save the day. Sounds like you are aware. 6 x $150 = $900.

Newer Z. 4:14

These videos seem to be popping up. There's some Datsuns. Here's one, looks like a B210. I had a 78 coupe, it was nice. Should have kept it. 2:44

If there's a cam there might be higher CR. You'll want to check things carefully. These engines are prone to detonation (pinging/knocking) and can get damaged.

And the 510. 4:04

I saw a Z and a 510 too. No fancy rev limiter crackling popping banging pseudo burnouts, just driving by. The 510 did try to make a bit of noise though. Not impressive. Found the Z.

Actually you're better off to have that "12V" wire connected out closer to the loads. Like at the battery. Connected at the alternator it will deliver lower voltage to the full system, because there's no voltage drop there. You have yours setup like a "one-wire" system. But that is all considered in the #14 link. One of the wires that is being jumpered is the "12V" wire. That's one of the things that SteveJ suggested you check. SteveJ has been doing electrical for years, but I was in and out of it and off and on myself so I might have more empathy. I tried a few of the connect the colors directions when I got in to old cars but always ran in to problems. Your best path is to consider everything and double and triple check. Trust but verify.

I was writing something when you posted. I'll go ahead and post it now. It's Reaganesque.

Considering what it looks like in the pictures I would make a video of the engine running and add it to your listing. Would probably help. And if you put the front struts and wheels back on somebody could roll it on to a trailer. The way it sits now, it will take a lot just to get it loaded. Just trying to help.

What is a crank vent? And a crank PCV valve vent line? Not sure what you're talking about.

Might be that somebody left the fusible link out and that is "real" wire. Anyway, I'd be wondering why it burned up. Maybe somebody connected the (A) B+ wire to the E terminal at the alternator. ZCD actually identified the wires on his web site. Not with proper terminology but still figurable.