What's missing? 727 BB

I like 71-73's the best. They had the wider front pump bushing that gives the front clutch pack more stability and old style front servo that shifted better. 74 and up are ok but they've got the new style load control front servo that I'm not crazy about but you can swap in the older servo from the one you have. In 76 they changed the output shaft spline angle so you gotta watch you don't mix in pre 76 rear planetaries with a 76 or later output shaft. They'll go on but will strip out under a light load. The front pump was also changed in 76 and requires a rear clutch carrier to match. They also changed the spline angle and pump again in the late 80's I think it was.

BTW: you could swap in a 71 style front pump and front clutch carrier to get the wider bushing.