If you are going to swap the trans i would also do everything at once. If you go to away from the L series trans you will be lining up differently. The newer series transmissions have different lengths. When I doubled my truck I just bought a crawl box(reduction case mounted to adapter) and mounted to my stock case and tranny. Was extremely easy, and could be done in an hour or two at most with simple tools. And if I do trans work, I would stick with the L series to keep it simple
