I'm just trying to keep it as neat as the original builder had it. I just sourced and added gain switch and ground lift switch, revised grounding.
Innie or outie… I think the original design was to use a larger chassis to keep trannies inside. Foam is just to hold trannies in place. I’ve seen some folks adhere the trannies to inside chassis with epoxy or gooey stuff. I don’t think the foam has any shielding properties, but cut a slit in it and you have a neat path for wiring. The white wire on Cinemag is connected to tranny housing so it is grounded as long as white wire is grounded. Bob and others mount trannies external with housing attached to chassis.