Interstate Motor Freight Systems trucks

I just bought the AMT Kenworth K-123 cabover. It has decals for Interstate Motor Freight Systems, trouble is, I have heard on several sites that they didn't use Kenworth power. What would have been a more likely  cabover tractor for IS trucks? I also saw a Louisville Line box truck used by IS. I have one, and it in the works now. Thanks for any leads/info.

Source: http://cs.scaleautomag.com/SCACS/forums/thread/980443.aspx

Chuck Weyant Ken Wharton Ted Whiteaway Graham Whitehead Peter Whitehead