I would go the 200-4r route (what I did) mainly because of gear spacing and BOP bolt pattern on case. You "should" be able to use your original crossmember and driveline (I had to buy a new crossmember and shorten my driveline since my original trans was a 2-speed ST300). Mine just uses a brake switch to lock out OD which is an easy install so it's not computer controlled. I went this route: https://www.bowtieoverdrives.com/catalog/catalog_inc/viewitem.php?ITEMID=12 and bought their TV made simple kit and transmission lines. The stage II is rated up to 450-500hp and 400-450 lb torque (which I may need to revisit with my new motor). If you do decide to go this route make sure you give the company your rear tire diameter and gear ratio so they can put the correct speedometer governor in the tranny so your speedometer reads correctly. Also, if you have a stock shifter you want to retain you can go to shiftworks.com and they have a kit to add the extra detents to your original shifter (I ended up going to an aftermarket shifter).