Rochester Carb
 

Is a Q-jet for a 305 jetted different than a Q-jet for a 350 - 400 ?
Bought one on E bay with intent on playing with it. Don't want to jack with the one on mine. Auction was jacked up by someone who only sells dried flowers. Go figure.

It's hard to tell for sure. Sometimes they were different for different engines, but also for different type vehicles. Most of what was different was the secondary side. There were so many different types of Q-jets, it ain't even funny. I recommend buying Doug Roe's book, Rochester Carburetors. This will really help you to better understand them.