take a look under any big rig on the road, all use straight axle, just dont ride and corner as smooth as ifs. But if you do decide to go the ifs route do yourself a big favor and just buy a mustang II kit that fits over your existing frame rails, by the time you are done fabbing and fitting and rebuilding a wrecking yard peice the price will be about the same.

there is no replacement for displacement?
sure there is, its called a turbo!!