Hey, Gray, welcome to Fordsix!
I found this place from a link at Inliners International,
www.inliners.org, so let me direct you over there for a moment. On the home page, look for "Rides", and go to that page. I can't remember the guys name, but he built a really nice blue kit type T-bucket using a Ford 240" six. Got featured in some national publications, and all that good stuff. He built it with his wife to show her how all of the mechanical parts of a car work.
Now that I think about it, there should be a shot in there of another T-bucket that was built by the owner of an Australian street rod shop, that also runs a Ford inline six.
Like Jack says, a slight frame stretch to cover the length of the two extra cylinders, and the rest is the same. If you can't order the frame stretched, a good welding shop should be able the splice in some extra 2"x3", or whatever, to get the distance you need. Have it added under where the body sits, and no one would be the wiser. They should re-enforce the splice with welded fish plates. Actually, I think a slightly longer frame would yeild a better ride, also. Go for it!
Later, Kinky6 8)