slant six turbo setup

I would suggest using one of the throttle body EFI setups, vice blow through carb. The price differential isn't that great, and they have so much more capability.

BorgWarner has a turbo match program:
http://www.turbos.bwauto.com/aftermarket/matchbot.aspx

So does Garret, it's called Booost Adviser, if this link doesn't work, just search that term.
Boost Adviser - Honeywell Garrett

Just doing some napkin level plugging, BW suggests an EFR 6758 or 7064, so you're looking at 54mm inducer/67-70mm exducer, ie a fairly small turbo. The EFR's are a pricey turbo, but the integrated wastegate, ball bearing journals and some of the other features are cool. Regardless, that's the size you're looking for. S/F....Ken M