Need help perfecting the budget build hemi swap

The next big thing, is wiring. Since I'm removing everything from one car, and installing it to another, I left all the components attached.
One thought is, it would be quicker to wire the engine compartment, and than unplug the MSD hemi 6 box. Than find a way to feed the 3.5" by 3/4" inch plug through the firewall. Thus the box could be mounted in the interior of the car. Since I have no intent on having air conditioning, I though I might feed the plug through where the air conditioning plumbing enters the interior.
On my 69 Barracuda the heater core tubes come through two round holes in a rectangular plate screwed to the firewall. I'm hoping that the air conditioning tubes mount similarly. I don't want to cut things, if I don't have to. The reverse way would mean feeding out several plugs with the labels I marked them with.
In this area, I'm up for lots of suggestions.