The Rochester 2-GC is an awesome carburetor; but running through a 2 barrel to 1 barrel adapter, you would be lucky to get it to run as well as the 1 barrel it replaced. We did extensive testing on these conversions many years ago, and found to come close to breaking even, the adapter needed to be at least six inches tall, and channeled. We never found any improvement by this type conversion.
To make the best of a very poor situation, make sure the float level is EXACT to specification for the specific carb you are using, by tag number.
If you plan to later install a 4 barrel, I would suggest doing very little to try to make a 2 to 1 work, and simply reinstall the 1 barrel until you are really to do the 4 barrel conversion.
Jon.
