I would get something in writing from SA covering what you were told. If you fire that commercial stuff and end up injured, you’ve got some recourse.
Then I’d stock up on the mil-surp fodder, and learn to reload if you don’t already know how. The Garand is a fine rifle but it’s never a good idea to stretch things beyond design specs too often.
That is my concern, although I think a bent op rod is the worst case.
I just need to go mess with the gas plug I guess.