Supersix - I cannot positively answer the question as to whether boring the hole oversize would help; as I do not have a manifold to inspect, and the shape of the plenum would be important. PROBABLY there would be a benefit by increasing the size of the manifold bore and using a larger single barrel carburetor, but it would depend on the plenum shape in the manifold.
As to the adapter, I seriously doubt that any benefit would be realized here. There MIGHT be a measurable (on a dyno, not "seat-of-the-pants") improvement IF you bored the size of the adapter using a taper attachment on a lathe, and reformed the taper of the adapter to the new bore of the manifold. I would doubt very seriously if this could be measured on the "quarter-mile", even in hundredths of a second.
The very best you will get out of the two barrel would be as Tony did, reform the manifold plenem to accept the two barrel without the adapter.
And one other thing I forgot to mention in my previous post: before doing any modification, run some type of "baseline" with your beloved Rochester B. You never know for sure if a modification worked unless you have a measurement. If nothing else, run three acceleration runs over a fixed length of road (when there is no traffic, and don't exceed the speed limit) having a friend time you with a stop watch; and average the three runs. Now you have a baseline.
Jon.
