City Friendly Diesel

I was considering buying this 05 2500 regular cab long bed truck that is for sale locally for $8K, its got 198K miles on the clock. I saw in the mag a few issues back about the regular short bed that they made out of the crappy V6. My idea is to section the frame and toss on a short bed and order a tom woods custom drive shaft with 1410 U joints. I have owned standard transmission diesels my whole life so I dont know how exactly to beef up an automatic transmissions. I plan on eventually have it pushing 600 or 700 horses. Would my best be to just pull it and send it off to suncoast and have them do it for me?  
1999 24 valve with Edge Juice w/ Attitude, Southbend Clutch, 5 inch Stacks, 4 inch down pipe, Bosch 40 hp injectors,and Fass Fuel System