1. do I need to carve another hole into the firewall, or can this be routed through the big, handy opening that all the wires go through?
I added that system to my 63 classic. The donor (I can't recall it) had a simple but odd system for passing the hose through the firewall: a short (3"?) piece of whiteish nylon rigid tubing, by memory 5/16" or 1/4" diameter. Onto this hose pressed the black rubber hose on each side.