I recently put an S10 chassis under my 51 Chev Pick up. I really wanted to use a Pontiac motor (and put Indian Head hood ornament on it) but this was a 'budget' build, and I was worried about space in the engine compartment.
The motor mounts I used on the frame came from a kit, but with some modifications, they work fine. I believe that the mounts will work for a Pontiac block as well.
Here is a link to my build, and there are more pics of how I had to modify the mounts.
https://67-72chevytrucks.com/vboard/...d.php?t=797726