best ford tranny for 68 mustang? help pls

sup everybody out there my father jus gave me his 68 mustang to work on while im at automotive skool and i was wondering should i go with a 5 speed 6 or stay with the stock 4 speed? i plan on putting in a ford 9" rear with an L.S.D. you can have all the HP in the world but if you dnt have the right tranny and rear end it's no use to get it to the ground. a friend of mine jus got a 04 mustang all he did to the engine was intake and exhaust system but he did work on his tranny and rear end and is doing burnout in 4th gear and fish tailing out of control. someone pls give me advice on the best ford tranny for 68's with SB and BB.

What intake and exhaust is that? I don't know of one that will add enough power to do a burnout in 4th gear. Also I don't think that the rear and tranny have much with getting the power to the ground. You need sticky tires and a good suspension to put the power to the ground.

sry i made a mistake my friend also has a high performance computer but im still lookin for advice of the best transmission for a ford sb or bb 68 stang

I would personally go with a Tremec T-56 it is cheap and a damn good tranny.