What kind of fab skills do you have?

I'm putting a Mercedes M104 in mine, but that's a long story and a giant PITA so bypass that.

How much of a OMFG it's got a "legendary" motor factor do you want? Most people go RB or JZ for the fact of having a 'legendary' motor and being unique. They've all been done a bunch so if it's comfy go for it.

ALL the current DOHC I6's are kinda weighty though and you'll be feeling the nose not wanting to handle, should that be on your list. If you want to get one from the mother land, your bill just doubled from a USDM example if not more, should cost be on your mind.

Ever though of an L28et? direct bolt in and you can easily get 300hp, which is quite a bit in a 2500lb car.

Moving on past I6's, I'm morally against putting 4 bangers in a car with a beautifully long engine bay once filled with 6 holes. Kinda like having long legs to run fast and shooting yourself in the foot, imo. You're also going to find that the SR may not be the best handling z as has been discussed on HBZ, as well has finding out it doesn't give you that huge million pound weight saving everyone fables about being all aluminum (it's a heavy a** motor for being all Al).

To the V8's.

The VH has been done. You can find one in a JY pretty cheap and adaptors are made to bolt the Z32 gearbox to them. You'll need to make engine mounts and fab exhaust but for the majority of swaps that should be on the list anyway. You get just north of 280hp at the flywheel out of the box and a crap ton of torque. They're heavy though, don't let the alloy fool you.

The VK fits. Nobody has done it yet, and I'm not sure why. It's a tight fit but it does fit. A few companies are making manual conversions now as well so they can drift their VK's. The 56 runs out of steam pretty early considering it's design even as a truck engine so if you could throw some JWT S1 cams in there that would help you out a bunch. That said, it's lighter than a VK and would make for a silly, disgustingly quick 240Z with all that torque. That's a good thing.

The Toyota 1UZ is the only motor I know of that's got more than 4 cylinders and comes in under the weight of a stock L series at 385 lbs. For the same price as putting the RB 26 in there mostly stock after it's all said and done you could have a fairly well built UZ running the R154 'yota box and turbocharged. These motors are basically the Honda's of the V8 world and love nothing more than to rev. Personally if I were considering this again, this is where i'd go.

Other things have been stuffed in there as well. A man from norway did a Viper engine, a few have done rotaries (a 20b would be nuts), a couple did a BMW V12 (if you put a Mercedes V12 in there you would be a madman, in a good way). And of course this is america so plenty of American V8's have been nestled it the ol' S30's loins.

Take your pick, pay your money, remember it's YOUR build and don't let the cool or wow factor from someone else influence something that you're going to have to live with, and have fun while you're doing it, that's what this is all about.