Ed, I've done the swap but an early 5 window roof to an early 3 window cab. It was fairly straight forward/not too difficult. But what you are proposing, as you're probably aware, means that the curvature of the 1 piece 54 windshield, at the top, would need to accommodate the forward edge of an earlier roof which was designed to use 2 pieces of flat glass. IMHO, I really think you're asking for trouble....there's little chance that you'll be able to seal the top of the 54 windshield to the earlier cab, and also it would look like c.... Not worth it. I'd keep looking for that 54 donor, or stick with the 3 window cab.
Good luck...Dave
