First off, it isn't a T10, it's a Ford T & C, aka, as a "top loader". It appears to be a small input transmission. GT500's are not 1-1/16", they are 1-3/8" and those stick out like a sore thumb.
I would also have a propensity of expectations to see a partial serial number stamped into the front edge with a Q engine code.
If the seller personally took it out of a wrecked '67 GT500, the driver must have been driving around with it in the trunk?