Slant six carb suggestions

It was either the Holley or a Carter BBS 1bbl. I don't know offhand for 1970. I am not a big fan of the Holley, and in general the 1bbl is a choke point for slant six performance, such as it is. I don't think a 2bbl adapter would get you much, either (you still have the tiny throat issue) — if you are going to solve the linkage and kick down issues with the 2bbl, you might as well get a 2bbl manifold — there is one for sale right now. With a Bouchillon kick down and a V8 throttle cable, you would be good to go.