The OEM 727 in the A100 was a short tailshaft unit and as such the driveshaft was no more about than 18 inches long. The A500 is a pretty long unit due to the extra length of the OD unit and the OD unit of the A500 will eat up most, if not all of the space the original driveshaft occupies. You might not even have room for a driveshaft!
I have a 727 here that came out of a 64 pickup with a /6 and the adapter plate, it looks as long as any other normal length 727 except it's longer by the length of the brake drum hanging off the back.