My 15-22 has a Weaver classic 1-3X mounted on a primary arms AR mount. This is a great set up. The last trip i only saw 5 squirrels, but had 4 head shots. The head shots were from 15 to 35ish yards. It is very easy for head shots with this set up. I was surprised how easy. I knew the gun shot great groups, but wow. My mod 60 might not ever go out again.
I don't think you need more than 4X for squirrel. My mod 60 has an bushnell 4X that does great. The Weaver 1-3X is more than i need. The Weaver has better glass.
The Weaver 1-3X is usually $170ish at MidwayUSA. If you use this months coupon code it is another $15 off. The PA mount is $25ish.