instead of using the PVC piping to fit into the intake boots why not make Intake plates that are drilled and tapped for the gauge and schrader valve? that way you could put the gauge and schrader vavle on the same plate and just make a block off for the other side? that way it would work for "stock" style engines as well as the race engine without a crossover.
3/16 plate would be plenty thick enough and cheap. just go to a machine or weld shop and ask for some of the "scrap" around the size of the intake ports. more than likely get the material for free. Cut the rough size with a hacksaw or sawzal, file or grind the edges smooth, Drill and tap for the valves Voila! bolt on leak down tester.
or better yet make intake plates for stock, cheetah and cub cylinders and cover the whole gamut of banshee engines.