I was suggesting you swap you `79 onto a `94-'97 460 equiped chasis. My '97 w/a 7.3 has ZERO room in the firewall department. Ford had no room when Navistar added the turbo, the downpipe is a piece of round tubing basically smashed flat. The factory set-up is VERY restrictive, but they had no choice, there's just not enough room between the firewall and the engine for the turbo exit pipe. They make a 3" round downpipe for the 7.3's (I have one installed), but you have to use a porta-power and crush in the firewall to make it fit.
My longwinded point is there's just no space available in the '97's, I'd think the '79's would be even worse (and forget it if you have factory A/C). I'm thinking a 460 equipped donor chasis would be way easier.