As I understand it, a 300hp/350 Powerglide car might have came with a 10-bolt. I am not 100% sure of this though, as I've never seen one.
Go here - page 36:
https://www.gmheritagecenter.com/docs/gm...vrolet-Nova.pdf
It shows a 10-bolt ratio with the 300hp/350-PG combo (3.08 vs 3.07 for all 12-bolt equipped cars). It also looks like the THM, PG, and 4-speed were the only transmissions offered in a SS.