Can someone tell me how to remove the metal recoil assembly from the plastic stock? I am replacing the crappy PTR buttstock with an original HK and in looking at exploded diagrams, I can't tell if it is just the two screws on either side of the recoil spring or if there is another screw that can be accessed through the ass end of the stock.

What Dano523 says about these rifles is true for the HKs ,but
NOT the PTR-91 US made buttstock.

The PTR buttstock has the buttplate glued on .
The PTR also does not have the 3rd screw inside the stock.

To remove the PTR buttstock from the recoil assembly;
Take the screws out of the recoil buffer ,
remove the buffer ,
place one half or the other in a soft jawwed vise or other
non-marking method of gripping it and pull /wiggle.

I got mine out by shutting the buttstock in my front door and
yanking the recoil assembly free ,but I didn't care about keeping
the original stock.

IMHO ,the flimsy buttstock on the PTR-91 is the only thing I
didn't like about my PTR ,and it was the first to go.