See if you can find the GM part number on your carb. I believe I've got an original condition carb on a 250 that's all complete and rebuildable. I don't plan to use it anytime soon. If I decide to build this engine, it's going to get some go-fast modifications including a conversion to a 2GC Rochester 2-barrel. IM or email me the part number, or the engine ID number, and we might be able to solve your problem.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!