727 trans.?

i just bought a 360 and 727 trans. and noticed the harmonic balancer on the 360 is like my 318 i was told i couldn't use the 360 torqeconverter on the 318 because the 318 is internalbalance and 360 is external balance now i found out the 360 came both ways internal and external so will it bolt up to my 318 ? i know the driveshaft has to be shorten what other problems am i facing stallconverters are so much cheaper for the 727"S