Another way to go if you are crafty is with Mega Squirt. It is a self built system that lets you use any components you could imagine. Mix and match. You could use a GM manifold and injectors, Ford throttle body and Volvo MAF sensor or what ever. The thing I like about it on my turbo VW build, I can control timing, timing retard under boost, timing retard with knock detection, run water/methanol injection under x pounds of boost, etc etc. If you are good with a soldering iron and even better with building maps this is a really cheap way to go. And I do believe you can control GM timing on a HVS distributor and should be able to on a 'small cap' HEI also.