Personally I would be afraid to try a "replacement" carb. Q-jets seems to be very specific to the application and would think that replacement would be "one size fits all" or at least one carb fits many. Might be close, but not exact.
I would get your carb rebuild, after confirming it's right/original. The problem is finding a competent rebuilder is very tough.
In the meantime, I would get another junkyard carb that's close. If you change it and nothings changes, it might point you in another direction. Or if things get better, you'll know it's the carb for sure before plunking down big $$$.