OK, interesting on the frame, just would not have guessed that it was factory - kinda amateur looking in fit and finish.
Bushings can be hard to remove, but as old and hardened as they can get, pressing them out may not be the solution. It would have been wiser to use a torch and burn it out, or at least melt it a bit to loosen before pressing.
The 1964 rear end is unique in that it uses the 1 year only smaller bushing and had a shorter upper control arm. I cannot confirm, but the upper control arms may have been designed with an eccentric so they are adjustable (this would change the pinion angle). I supplied a couple pics from the web. These are Chevelle, but it was noted that they were used for other GM A-body cars.
The Pontiac 8.2 10 bolt gray iron cast center housing should have casting #9773369
. However, I found this on Ebay, 1963 cast rear end dated September (I) which makes it a 1964 rear end. It has casting #9773722
If you find a rear end, the 1964 Chevelle also uses the same smaller bushing. The Chevelle forum says Autozone sells the Duralast brand #FB295
bushings, they're $5.99 and they're the right bushings. The FB295 is the front lower control arm bushing for a 73 Camaro with a 1.375 OD.
The PHS documents for your car should tell you the factory rear axle ratio? My info says the W/AC & auto - standard ratio is 3.08. Optional 3.23, and 3.36 optional with the "77" engine only. Without AC on either manual or auto - 3.23 standard ratio on 78 & 79 engine, 3.55 standard ratio on 76 & 77 engine. Other ratios would be optional (3.08, 3.36, 3.90) to include dealer installed ratio's - 4:11, 4:30, 4:33.