So if I have a 68 727 with the original TC and I have a 76 440 does it need some modification for the external balanced engine. I am not sure about autos.
There use to be weight kits with destructions available, but I haven't seen them in a long time. I usually end up with a b&m flexplate and a neutral balanced converter.
Yes your 440 is externally balanced so it either needs weights or like George pointed out the B&M flex plate to balance it. I almost always go the B&M flexplate route cause it's so easy. Here's a link to the B&M flexplate on Summit