The front of the 904 or A-500 can be built with enough strength for 600ft/lbs of torque without using many aftermarket parts. As to the O/D unit, the A-500 can be upgraded to 518 parts - my buddies trans shop has done many of the A-500 RH40 units and swapped in 46-48 O/D clutch drums. As to the 200R4 - 700R4 debate, it doesn't really take any more parts to make a 200R4 take that kind of power than a 700R4 does, and the 200R4 is lighter and smaller than the 700. It also has the same gear ratios as the A-500, so it doesn't have the big RPM drop as a 700R4. Thats why I like the 200 over the 700.