Simply from a reliability/accuracy standpoint, is there any noticeable difference? Found an HK91 for a "reasonable" price.

Buy it. If it's a good price, you'll never lose a penny.

You can always ask that question later.

Buy it. You might regret it if you don’t.

91’s and FAL’s have a certain allure.

IMHO - no, the PTR-91 was built to take advantage of the scrapped surplus HK-91s, you’re typically going to buy HK branded parts to repair/replace anything on the PTR.

My only compliant with my PTR GI was heavily used HK ODG stocks, on a “new” rifle.

It went bang with everything I put in the magazine, but just lost interest in it after a while.