All the 360's were external balanced. 1971 was the first year for the 360 and is supposed to be a stronger block than later years, but not an issue for a mild motor. The B&M flexplate for the 360 (balanced with the engine) will allow you to connect up any normal balanced torque converter.
I built a mild "RV" type 360 for my truck, 9.5:1 compression and an older Hughes Engines cam, around 215/220 duration @ 0.050", and a bit over 0.500" lift using crane gold 1.6:1 rocker arms. Stock "J" heads with 2.02"/1.6" valves and alot of bowl porting and some porting of the runners. Gasket matched to a standard Edelbrock performer intake and 670 Holley Avenger carb. Runs real good, but if I was to do it over I would just use some better heads like the Hughes Iron Ram heads, they flow better and have better combustion chamber design.