Since you're in the hunt for a 727 convertor, in addition to the exceptions I noted above, you need to avoid the '67 and earlier TC, since those had a different input diameter and spline count, in addition to a different convertor nose diameter.
Lockup convertors started showing up in some (not all) 727s in '78, lockups are again unuseable in your base 727. Lockup/OD trannies (A518/46RH and later the 46RE) started showing up in '88- this is the TC you currently have and can't use.
So, your useable window for 727 convertors is '68-'88, avoiding the lockups.
Happy Hunting!
