Hotwire harness

Helping a friend do a 5.7 into a 72 Challenger. He got the Hotwire Hotrod harness. Says harness needs to go through firewall right behind and slightly below the pass fuel rail. Down behind the head. That looks like it will be going right into the A/C heater box. Need your help.
I know I'm no the 1st to run into this.
Thanks

I am running the hotwire hotrod harness in my 1957 plymouth. I punch led the hole as instructed, and there is NO harness length to spare if you plan on using the supplied firewall grommet. it makes for a tidy install, but there isnt any room for playing aroind with location.There is length to work with once you get inside the passenger compartment for attaching the computers. Sounds lime you will either relocate the HVAC, or punch the hole elsewhere and find a alternative methos for sealing off the surrounding area.. you could cut up the harness to add length on the engine side.... but I didn't have the stomach for it.

Mock up the harness on the engine and see where it falls in relation to the firewall maybe??? Just an idea

Looks like we are going to use a Vintage Air box so that should give us the room we need.
Thanks guys.