NewZed

Don't overlook the fore and aft movement. The bushing sleeves and bolt length and nuts and washers all need to be considered. There are no clear exploded views of how all of the parts there fit together. You kind of have to mental it all together.

What's the bore size of the T3 parts? With a tight tolerance and some grease it becomes more of a bushing type application. I think the original pin is 16 mm. 5/8" is loose. 5/8" = 0.625" = 15.87 mm The lock pin allows the bushings to perfom their spring action with vibration damping, and also keeps the arm legs (?) connected if the nuts come off. If you switch to the PU bushings there's rotation inside the bushing anyway. If I was using a 5/8" bolt I'd probably just safety wire the nuts or create a flat and use a peenable nut. Just for peace of mind. Just some thoughts. A bolt and some threadlocker and you'll probably never notice a difference.

Can't tell from your pictures if the brackets are swapped. The engines have a tilt to them with proper installation. If the brackets are swapped I think that it does bring the left side up, making the top of the valve cover more level. It can look correct but be wrong. The simplest way to tell might be to check the bottom of the oil pan. It should be level from left to right. Hate to say it and maybe, subconsciously, you already know it but it looks like that custom intake manifold could also be the problem. Where did it come from? Good luck.

Make sure you get a 280Z mustache bar to use with that 280ZX R200, it's needed. And the half-shafts if you don't have the clip-in style. Not clear what you're starting with. The other part of your "old posts" problem is parts availability. They're not as plentiful as they used to be. The 5 speeds and the R200's and the required mustache bar are getting harder to find. You can go aftermarket on the mustache bar but it's expensive. Finding parts might be your decision-maker. A junker 280Z might be a good way to get the parts. Good luck.

These words don't make sense. The valve cover is hitting the intake throttle body? Not sure what the effect is but sometimes people get the left and right engine brackets switched. I know it changes the angle of the engine. Not sure about height. Parts 6 and 7. https://www.carpartsmanual.com/datsun/Z-1969-1978/engine-280z/engine-mounting

Get it running and drive it. Probably not worth restoring. They are easy to work on. Service manuals are available to download on several different Z sites.

It will be interesting to see how things hold up. Are you using MIG welding? I assume that you are but you didn't say. There should be warping at each weld spot which might affect bearing wear since the inside of each cap is essentially a bearing race. Besides loss of heat treatment. Not trying to be negative, just assessing the odds. Good luck.

@Dat73z If you wanted some discussion about your recent post you'll have to post in a non-FAQ section. People can post new stuff in FAQ but nobody can reply. It's been this way for years, not clear why nobody fixes it or at least adds a note to new posters. You didn't say which u-joints were "too soft". That would be helpful.

Don't overlook the shield.

Might have better luck on classiczcars.com. More traffic and there are some parts traders there. Good luck.

Bumping zboi's thread so he can continue his contributions to the community. Let's see an update.

The internet is a great place to learn. Learn first, then speak. https://www.investopedia.com/terms/e/economiesofscale.asp Where are those dyno numbers? If the engine still runs.

I don't have Megasquirt but I know a little bit about EFI. Don't the MS data tables show injector open time? Duration? If open time isn't at 100% then it's not the injectors, it's MS not commanding them to stay open longer to provide more fuel. If they are at 100% then increasing fuel pressure should increase their flow rates. Sometimes on problems like yours it helps to break things down to the smallest elements. Analyze each step. What should happen versus what did happen.

RTPD = Read the post disappointed You should have created a fake name that at least leads to the mystery company. https://www.google.com/search?q=Flex+Engineered&rlz=1C1SQJL_enUS862US862&sourceid=chrome&ie=UTF-8

This part of the Megamanual might help. https://www.megamanual.com/begintuning.htm#spark https://www.megamanual.com/ms2/tune.htm