From my books
63-64 pump and motor assembly #4461121 sup 4888528 fits full size Chev ( other years different numbers )
63-64 pump and motor assembly #4461121 sup 4888528 fits full size Cdn Pontiac ( other years different numbers )
64-69 pump and motor assembly #7595117 sup 442949 fits Beaumont ( and I'm almost certain Chevelle and other A bodies )
the 63 Acadian catalog only gave a listing for 63 and it was again a different number.
I'm also suspecting that your unit will fit other GM full size from 63-64
Lefty, from what I see the main difference is your car has a three point mounting bracket. I don't have a convertible to look at but I seem to remember the 62-63 Acadian/Nova has one mounting hole on the driver side and two on the passenger side. The hydraulic pressure requires these to be tightly mounted to the shelf and that is what the rubber mounts provide.
The wire harness connector looks the same. The black end is motor and it must mount to the same side as the original. The best place to buy these pumps is in Punta Gorda, FL and I drove over there a couple years ago while wintering in Florida. I think I paid about $200 for a new one direct from the manufacturer. When I attemped to install it later, the motor was at the wrong end in relation to the single mount and I had to take another drive over to exchange it for one with the motor positioned correctly when utilizing the factory holes on the shelf in the trunk. These people are very helpful and good quality product they stand behind.