Personally I had a local shop do a complete rebuild with good clutches, koleen steels, wider OD band, transgo AOD-HP kit with high rev govener, and all the goodies. I bought a hardened input shaft and an Edge "Mild Street" converter to with it.. should handle 450-500 hp without any problems and it was a LOT cheaper than buying one from one of these companies like Lentech.
If you did just want to buy one all done up you may want to look at these guys though.. I bought my input shaft from them and liked the service I recieved. http://www.ford-aod.com/#Performance Parts