Can anyone tell me what would be the min. chamber/barrel wall thickness for a 22 LR. I'm trying to plan out a new project

Probably thinner than you could work with. I think it was Hatcher that turned the barrel of a 30-06 Springfield to right at a 1/16" wall over the chamber. This barrel still withstood normal match load firings and was not damaged untill a 75,000 psi proof load was fired.

While certianly not recomended the 3/8" dia. liners for renewing shot out .22's are suficient by themselves. I'd feel a lot safer with at lest 1/2" though! Look at the new composite barrels (w/ liner) and the wall thickness on some small (cheap) revolvers. However the chief issue is stiffness rather than safety, unless of course accuracy isn't a concern.