probably a dumb question but...

I wouldn't go with just one ring. That wouldn't be secure enough. B-Square make extension rings for .22s with grooved receivers that provide 3/4 inch of extension.

I agree, extension ("back swept") rings are your best option, and should work fine.

Go to brownells.com and order a 6" piece of picanty stock and drill it/have someone drill it to fit the reciever for you. That should take care of that

Assuming Mossberg Chuckster with 3/8" Weaver-style tip-off mount grooves

The 3/8" grooves for Weaver-style mounts are different positions on every .22 rifle I have owned; I have had to select different scopes (in 3/4" 7/8" and 1" diameters) for different receivers based on the design of the tubes allowing rings to be placed in positions compatible between scope & rifle for proper eye relief.

There is a extension base for the Winchester 9422 rifle that fits the 3/8" receiver grooves to allow both 3/8" '.22' tip-off and regular Weaver 'biggame' detachable mounts. It also raises the scope about 1/4". That could be a possible solution IF it does not interfer with the Chuckster bolt handle.

ADDED: if someone makes a Picatinny rail extension on the same principle as the 9422 mount, it would be a big help to owners of .22 rifles with the standard grooved receiver.

www.bkltech.com/category_s/57.htm?searching=Y&sort=7&cat=57&show=9&page=2

BKL #274 Off-set mounts may work for you.