So, I'm not familiar with the Pro R or how much clearance there is between the plug and frame. I'm just curious... Was the Allen socket hitting the frame or the extension? Were you using 1/4" or 3/8" drive? Surely, Polaris would provide enough clearance to properly torque the plug (sarcasm). LOL
I love the Allen ball ends but they don't have as much grip if you need a lot of torque.
If it's the extension not clearing the frame, I'd try using a wobble extension.
If the 8mm Allen socket clears the frame but won't fully seat in the plug, I'd try a 5/16" Allen socket. It's about .003" smaller.
If the 5/16" Allen socket clears the frame but won't fully seat, I'd try "tapping" it with a hammer.
If an Allen socket won't clear the frame, I'd cut an Allen wrench to length and put a wrench on it.
And if all that didn't work, I'd smack the f*** out of it with a brass drift and use the Allen ball end or a cold chisel and hammer. Then, I'd order that $140 drain plug kit. LOL