What tranny is my best choice?

He is NOT selling a 360 "HEMI". No such animal. From a 2003 he either has a 5.7 Hemi or a 5.9 (360)Magnum for sale.

You didn't mention what engine or transmission you have now, I'll assume a V-8 of some sort and a 904. Either engine will bolt to your current transmission. A 904 in good condition will live OK behind a mild 360 or late HEMI.

The 727 is a heavier duty stronger transmission. It was used behind most all 4bbl small blocks in cars, most small blocks in trucks, and all big blocks. International Harvester used it in their light trucks and Scouts, Jeep used it from 79-91 in Wagoneers and trucks. An overdrive version of this transmission was originally in the 2003 truck. They bolt right into A-bodies (63-66 requires slight mods)