Still trying to figure out what to do for a body for Big Al. The Freightliner cab and cockpit slide right down over the frame rails, and would look particularly good with a top chop, especially with the menacing-looking visor over the windshield ... bodywork below the level of the door would be cut away, and the exhaust would simply go through a right angle before dumping. I like this better than the Ford T pickup cab, but a simple T-bucket cockpit, with a gas tank on a platform over the rear axle, is probably more appropriate.
Decisions, decisions... meanwhile the chassis needs to be lengthened to fit the Allison behind the radiator, and to get that long, low look -- the Freightliner wheelbase looks to be about 124", not too far off some of the bigger American boats like the '59 Caddy. So before cutting into any bodywork, I spliced in about 15 scale inches, using Evergreen 0.060" sheet stock. I also built wedges to get the engine at the right angle.
Overall it is still looking good but for best effect, I think lowering the chassis significantly over the axles would be needed. It is sitting far too high for a proper rat rod. I'm going to stop here and ponder the major surgery that would be needed to do that.