12 FV stocks are for hidden magazines and unless you want to open up the mag well and replace the hidden mag, you would be better off looking for a replacement that will fit the 10 FCP detachable mag.
Someone who replaced stocks on any older FCP might be a source for a stock, but some newer FCPs were made with accu-stocks and bolt releases in front of the trigger guard.
There are lots of stocks available for top bolt release Savages that are set up for detachable mags.
I believe that Bell & Carlson makes more than one model that would fit a Savage with a detachable mag.
Also take a look at Boyd's and Stocky's sites to see what other possibilities they might have.
I would recommend you choose a stock with aluminum bedded posts.
Aluminum bedded posts provide improved stability over a factory plastic stock without aluminum posts.