I used an 87 GN turbo. It is a TBO348 (also used on 86GN's as well).
Here is the compressor map.
http://www.turbobuick.com/forums/turbos-turbo-related-parts/247569-stock-tbo348-compressor-map.html
Good enough to get a stock slant (with a few minor changes) into the 12's.
Tom