What Scorch said.
I have Eight Rem 722's as I'm collecting them, and have not seen a prefit pad for those rifles.
In order to maintain the Rem 721's intrinsic value by keeping the stock original, you might consider getting a Rem 700 stock for the rifle and installing it as a shooter, leaving the 721 stock original. There are a lot of Rem 700 stocks for sale lately at reasonable prices.
US Army Retired
NRA Benefactor Life Member