If the frame behind the cab is not to your liking, and you have access to a
c60 frame, you can probably cut it and splice a piece of the C60 frame onto it. If you fabricate a glove for inside of the frame and then V out the splice and weld and grind it, it will look nice and be strong. If you are going to subject it to heavy loads, a cross member at the splice and a fish plate over it wouldn't hurt anything. Frames are stretched like this all the time
