Frames are identical except for the front cross member and you will probably be removing that. If not, you can grind off the rivets to the frame and exchange the Chevrolet one for the GMC. That's what I am doing but in the reverse. I have been looking for a cross member for the GMC, so i can use the chevrolet frame.

Another difference is that the 53 uses bendix brakes and tube shocks whereas the 49 uses huck brakes and knee action shocks.