Depending upon the year model, some of the internal components "may" be different, I'm not really sure. I had a BB 727, RMVB, no low band apply, with trans brake & a 5000 stall converter. I swapped it all over to a SB 727 case with no problems. I hope it all works out for you.
I just picked up a motorhome 727 tonight. Hopefully this will be my answer. I will tear it down tonight and see what she looks like. If anything at least i have better planets now haha