I wasn’t concerned about hiding wires that you’d see on a stock harness. I just didn’t want any non-stock holes on the firewall and my solution seemed the best for me. I will still have some non-stock wiring - from a pushbutton switch to drop the trans out of OD and lockup and wiring to a couple of pressure switches to activate the OD and lockup - 2 separate functions with separate wiring or each.
I have read how firewall wiring had been successfully hidden inside the frame rails.
I’m sure I’ll see how you do this as I’ve been following your progress from the very beginning