[Super73]

I would suggest an water/air inter-cooler.

When I was going to go twin 67's my plan was to use two 4 1/2" thick 16"x10" cores inside an alum sheet metal box. The cores would be standing 10" tall inside the sheet metal box with aprox 12" between them. This 12" gap would have an alum shield so you could put ice in from the top it with out damaging the cores, then close the lid. Each core would have it's own input and output but they would merge via a Y connector, 2x 2.25" in and single 4" out.