IRS/body drop/air susp. opinions wanted

[HOOPTY67]

i've got a 67 chevy shortbed fleetside truck with a small block, 3speed w/granny gear and 12-bolt rear end.
I want to lay the rockers flat on the ground with 20-inch wheels and about 28 inches of tire. I pulled the body off my frame and after looking everything over i decided to build a 2x4-inch rectangular tube chassis instead of modifying my existing frame. Im going to use a Scotts Hot Rods IFS for teh front suspension and am looking at using a 1993 Ford Expedition, 1992 Toyota Supra or 1999 Mustang Cobra IRS differential with custom shafts and arms that i would fabricate for the rear suspension. I'm hoping to make the truck handle better with the IRS than a solid axle. The ford rear diffs i'm looking at have 8.8-inch ring gears while the supra has a 7.5-inch gear. Im sure either will stand up to 500hp,which is about how much i intend to make.
Anyone every adapted IRS to their trucks with air suspension and how much travel were you able to get out of it? Looking at older corvette IRS with u-joints it seems they wont be able to get as much suspension travel without binding.

I think i need about 10-12-inches to get the truck up high enough to safely drive it.

oh and if anyone needs a shortbed chassis, ill be getting rid of my complete chassis, rear end, tranny and suspension etc for cheap.

thanks!