The biggest problem is the Floor Hump. The Factory 3-Speed truck will have a Low Hump on it and the truck 4-Speed requires the High Hump. That reason alone has made me decide not switch some of them through the years. If you have a good garage, a welder and a good High Hump Floor section available, it would make it an easier project.
I believe you would also have to change the Bell Housing as the 4-Speed trans should require a larger Input Shaft Housing Opening. You also may have to change the length of the Drive Shaft.
Bill
