Take a look at this post I would use the original 72 mounts and build brackets off the frame to fit somewhat like was done for this Buick engine
http://67-72chevytrucks.com/vboard/s...d.php?t=703223
Here is the 72 Pontiac mount (drivers side) with pics
https://www.napaonline.com/napa/en/p...243_0513157797