Good question ....
Weaver does not show bases for the X7, but Tally does show LW bases for the XL7. I'm sure they would fit on an XS7. I'd call Marlin to see what Weaver if any would fit and/orTalley to see if the XL7 LW set will fit the XS7.
I've had a couple Marlins with the 1pc base and found they worked great. They offer a lot of flexibility for scope location. I'm not switching mine out based on that.