don't throw anything away until the new wiring is finished, then offer any useful bits in the swap
not sure how you'd use fewer than stock firewall holes, considering most of the wiring uses one main hole, and the manual choke, throttle, oil pressure tube and speedo cable use 2 others - maybe your's has had a lot of PO modifications made?
the original style repro harness is the easiest to install, all lays out like the factory diagram and with the proper colors and connectors for everything, a 'generic' harness might have the extra length wires you'd need to reroute things, if you're confidant of ability to install the end connectors and wrap a cable neatly
Bill
