tuff5liter

I have a 5.0 with 346hp/353ftlbs. and i am still running my stock t5 transmission. I would like to switch to an automatic, but im am not really familiar with the transmissions that i can just go pull at a junkyard and install and not have to change my computer or anything and if they will be able to handle the power i have now and the potential power i want to make. I have the current numbers NA, with a basic 302 ( i just have a rebuilt SB, afr heads, trick flow intake.....). I saw an article in MMFF about the 5 speed transmission in the S197s the 5R55S and the correct kit to beef everything up. I am not sure if that particular transmission will fit in a fox, BUT that is what I am looking for. Something i can get at a junkyard and beef it up as i have time THEN install it once i finish the beef up process. Any ideas would be greatly appreciated.