The spacers won't be needed, it will run better with more heat as the aluminum dissipates the heat much faster the iron. You will however loose drivability if you try and run two Rochester's. You need two carbs that match and are much smaller then what the engine came with. I run dual W-1 Carters made for a 216 on a 250 inline six. I tried two Monojet's that the 250 came with, it would run, idle, and make decent power, but I could see the fuel gauge move as I was driving, I am talking single digit fuel mileage!
