I have found the best way(for me)is to find 2 pieces of 8in. or 10in. channel iron a little wider than the truck,put bare wheels on the truck and set the wheels in the channel.Use angle iron or pipe tack welded to connect the sides.If you want to add the 1 1/2 inch just mark your angle and slide the channel forward before you tack it.After you cut the frame set the clip with bare wheels on it in the channel and weld every thing up.

_____________
Floyd

If we choose being kind over being right,we will
be right every time.
Knowledge is a poor substitute for experience.
Remember what is precious to another, may not be to you, but it
is precious nonetheless.

1948 Chevy 2-Ton