Trying to use a stock Air Cleaner 2 Barrel and convert it to a 4 Barrel.

No matter what, I would run the original diameter filter. I picked up 1/10th ditching that filter for a 12” diameter one. If you were closer, I would spot weld it together for you. So looking again that is the stock diameter. Larger would be better even though it brings it closer to the outer wall.