soba_03,
Unless this is something 'new', the linkage from bellcrank to the piece supplied by Offy is just a bent piece of 1/4" rod.
Bending it so that it allows full throttle and closed throttle takes some work, as the space through the manifold runners isn't very large, plus the bellcrank tends to make the motion of the rod forward and backward as its point of connection at the top has been moved..whew, what a sentence!
The Offy linkage that connects the two Rochesters is poor at best. Be sure to fasten it to the arms on the carburetors very well. Getting both carbs to open evenly and to close properly can be a real big chore. Good luck.
Stuart
