How hard do you think a f20c in a crx would be

[speedminded]

K-series in the back would probably be easier and cheaper -- no guarantee on handling though.

Nearly stock K20a2 in an Elise, 0-60 in 3.7 seconds...
http://www.prototyperacing.com/k20kit.htm

I want to do an NSX with a built turbo K-series