[Bruce Lancaster]

If the screens are the problem, you need air cleaners with more flow capacity. I do know that many of the small dome/paper filter types most commonly used are completely inadequate, working as chokes, and I suspect that the good ones are probably marginal. With 2 cars over the ports, you have some room and might be able to adapt a pair of the smaller four barrel sort and be able to find name-brand paper filters with enough area.
Also, has car been driven in warm weather and run long enough to fully warm the engine? A distant possibility is the racing manifold with no heat crossover.