A500's are 2wd trannies. In order to do the swap you will need a crossmember from the donor vehicle, and a switch for the lockup and or overdrive. I would recommend using separate switches, but it doesn't really matter. I think the A500 is longer than the 904, so you may have to have your driveshaft shortened.
A500's are 904 based trannys, A518's are 727 based trannys. Basically, the newer trannys are the old trannys with an OD unit on the tailshaft. I am not positive, but I believe the newer 4x4 dakotas use an A500.
The 518 is stronger, but also has more parasitic loss. An A500 with some internal mods should live happily behind a motor putting out up to 300 HP.
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