4r70w Swap Or Aod Rebuild?

let me give you a third option, how about a 200r4 swap? advance adapters makes a kit for the swap, and a 200r4 can be built to handle high power levels, and wont burn out the overdrive when you run full throttle up shifts into overdrive.

what year is the aod? if it's a later one with the stamped drums, and you have the mechanical ability (and the tools) to rebuild it yourself, i'd go that route. the 3.8L 4r's have a clutch or two less than the v8 models, and im not sure would be able to handle 400hp without adding in those clutches (easy to do, they just use a thicker spacer in place of the clutch). other than the input shaft (and the older 1.5" od band with the cast drums), stock aod internals can handle 400hp or more pretty easily.

the 4r internals can also be swapped into the aod case, and either way you go, you'll probably want an upgraded converter, od servo, valve body (or controller for the 4r unless going full manual), and the aod would want an inner input shaft. that all adds up fairly quick, and would probably even out the playing field.