The Harper 3x2 setups worked. There is a thread here about them. They used 3 97s with the throttle shafts split. One side on all three carbs was the primary circuit. The other side was the secondaries and they were progressive. The linkage was complicated but Jalopy45 here has successfully made some for one of his. The manifold itself is three 90 dredge elbows with a small balance tube between. They are one of the coolest, most mechanical, Rube Goldberg looking pieces of inline speed equipment ever built and they work.
Search Harper on this site if that doesn't work go to Jalopy45's page and search his posts.
