If I were to do any type of swap, I'd go with an all aluminum V8. It would probably be easier and cheaper to swap the complete drivetrain from the corvette instead of trying to mate another Honda engine to the stock drive train.

400hp NA from a screaming LS1 would be awesome. Instead of a Monster Miata, it would be a Monster S2000.

 

An NSX motor? Just think about the pain it would be to make a Mid-engine platform motor fit into an FF...

It sounds like your friend wants some balls out torque. Go with a K series hybrid, since your mounts are already K series mounts in the first place. The clearance issue might be a problem, but if you can afford an NSX motor than you can afford this beastly setup:

Do the hybrd K24 motor swap. Source the block from a TSX (2.4 liter block) and use the head from a RSX type S. During the buildup process you can actually put in aftermarket pistons, rods, bearing, valves, retainers, valvesprings, head gasket, and other stuff. Think about it 2.4 liter with VTEC, that thing would be a beast on the streets and you're looking at a lot of money and time to do that swap. But it has been done before and it surely is the next sleeper hybrids that people are doing in the honda world.