Will Chevy 400 small block bolt up to 1990 300zx transmission?

No, a Chevy 400 small-block engine will not bolt directly to a 1990 300ZX transmission. They have completely different bolt patterns and bell housings. You would need an adapter plate specifically designed to mate those two, and even then, there would be significant challenges involving the different input shaft dimensions and potentially the flywheel/clutch setup. It's a major undertaking, far beyond a simple bolt-on swap.