I called Limbsaver and CS asked a couple measurement questions. She immediately said the "Medium" #10551 was what I needed.
Picked up the size at Walmart and it fit snuggly, but not overly tight. I think for plastic stocks it could of fit a bit tighter, but these were designed for those rifles or shotguns that didn't have rubber recoil pads, wood stocks, needing 1" extra LOP and was made to come off easy to not harm wood due to holding in moisture after damp hunts. Rifle fits my arm length better with that extra 1" LOP.
Do watch out, Limbsaver does make a "Small-Medium" in which the dimension at the heel is just around 1/2" less lengthwise and 1/2" recoil pad instead of 1" that the regular Limbsaver uses.
I also picked up and installed a stretchable buttstock cartridge holder (holds 9 rds) to not carry around another 10rd loaded magazine, which could be lost accidently when out on a hunt. I have a few of these cartridge holders on other plastic stocked rifles and they work very well. A little softer on the cheek weld too. I recommend.