Here is a cross reference - scroll down to GMC and note several other Zenith model number carbs for 270's.
https://www.carburetion.com/industrial/zenithcrossref.aspHolley also has a 270 application - but I am not familiar with the reputation for these Holley's. I have a NOS GMC 270 Holley on a shelf here, but plan to use that as a back up - or just to test it someday when I have nothing better to do.
There is a 2 barrel Stromberg WW carb for the 302 (or even the 270) that might be a good option for you. Would be interesting to read Jon or Jon G opinions about the Stromberg WW (or the Holley for that matter) My impression is they are very good carburetors too. I have one on a 302.
Keep us updated about your 302 rebuild. I would like to follow your progress on that, and I am sure others will too!
