Well, I've been looking at used DOHC engines. It looks like it would be easier, and may very well end up being cheaper as well, to build a one-off supercharger kit.

You can get the DOHC engine for as cheap as $700-$800, however I'd be leary about installing some else's engine without rebulding it first. That's what would make the DOHC swap more expensive. Even just using the heads, I'd want to rebuild them.

The supercharger would not require swapping so many parts.

FYI, I've seen M90 blowers mounted on N/A 3000GT's. I forget who produced the kits. I used to want a 3000GT so badly, until I realized the SL was FWD.