Hello Joe!
I'll be watching this one with interest. If you want to treat this baby with your usual attention to detail, this is going to be a long project! Those AMT kits are factually very correct, put the parts tend to be very crude. On the other hand the Italeri kits have nice detail, but some of them are pure fantasy - the worst is probably the "Power truck" or Mack Superliner. For example, instead of a Mack frame and suspension it has... a Freightliner frame and suspension! This could be useful for you. Almost all of the Italeri 1:24 trucks have a Freightliner frame.
But first I wanted to invite you to take a look at my Mack Superliner build thread, to give you all kinds of wrong ideas... Please note that this build is still not finished - that's exactly what happens when you go too deep with a project. But I have it stored and I intend to finish it one sunny day:
http://cs.finescale.com/fsm/modeling_subjects/f/4/t/127400.aspx
And here's a reference for you:
More like those are easy to find just by googling "Freightliner frame" or something like this. The thing is Freightliner started to build trucks in the fifties and their basic frame and suspension design stayed the same for decades. So the cutoff from a 1986 truck will be almost the same as in your model. One thing to note is the air ride - they started to build air bags instead of springs some time in the seventies, and since this gives you a lot better ride the air ride is now way more popular than the spring suspension. So here's the idea - maybe you'd like to transplant the Italeri frame to your model? This gives you much nicer detail, air ride and positionable front wheels to top it off - what do you say?
And you should know that the drivers didn't regard the Freightliners very high. In their slang they are called "Freightshakers". A one man company driver wouldn't rather buy a Freightshaker - more likely a Paccar (Kenworth/Peterbilt) for comfort or a Mack for ruggedness. On the other hand a fleet owner would be glad to buy a couple of hundreds of them Freightliners. And now the company is owned by Mercedes of Germany.
Good luck with your build - I will be watching - and have a nice day
Paweł