Before you get into shell-swapping, and I do not know what version of the Weaver RS-3 that you have, but can you determine exactly what in the running gear (and perhaps interior motor movement interference and/or wiring) is causing whatever problem that you have, then do a bit of careful modification (filing, etc.)?
I'm just winging it; you may have already investigated this.
A brand-to-brand body swap can be pretty easy...
Or not.