When ever I see a setup like that there is not much going on power wise in the outboard cylinders. The angle of the roof is way too steep for the correct flow of air and the fuel to go with it. Twin carby it and there will be zero issues with that stuff. What happens is exhaust reversion builds up in the corners, and depending on the firing order and cam selection as to how serious it gets. It usually shows up at idle and the immediate response parts of driving, once its underway its OK but its still lost time on the strip because the engine has to recover from idling. It takes up to 4 seconds for a small plenum engine to recover a contaminated manifold to fresh air again. Seen it do that many times.