i assume everyone who's interested in reading this is familiar with the nissan 240sx/silvia- referring to the s13 model here.
over in japan, a few variants of this model, the Silvia Q's line and the 180sx, used the CA18DET engine- different and smaller from the SR20-series nissan engines i'm used to working from, but still revvable, and fitted with a turbocharger to boot- so yeah, they have potential.
this engine was brought to the states for a *few* years, but not in the S13 body- it was used in the earlier 200sx, back when it was rear-wheel drive- but the good news is this model existed until 1989, which is the same year the s13 was first brought to the states-
this gives you the two ingredients you need for a CARB-legal engine swap, which are having both the engine and the body US-legal for the same year (or newer on the engines- updating is legal, back-dating is not).
overseas aftermarket support for this engine is extensive- 250hp would be had easily with extra flow, fuel, and boost, but the recipe for making turbocharged vehicles is fairly well established, so no need to go into the details here.