Driveline hanging, maybe not brakes...

[71GFER]

As I've been trying to chase down the rear brakes hanging, I'm beginning to wonder if the issue is in the driveline. Is there anywhere other than the parking brake that could cause the driveline to hang? (and get worse as the car is driven) Has anyone ever had an issue with the parking brake hanging? Just in case I loosened it as far as I could since the owner didn't even know it worked and told me it wasn't hooked up. (or I would have checked it first)
Its is a 71FJ 3speed with stock driveline, except the motor (400 V8). Can these drivelines handle the power of a V8?

 

[3_puppies]

with a V8 you would drive thru the park brake without issue.
most likely, if I understand the qustion above is the rear brakes are being applied and slowing/dragging? the issue is in the brake master/booster.

your weak link will be the trans and transfer.