Another alternative, if you could live with an unused hole in your bullpup stock, would be to remove the OEM gauge and extension and plug off the gauge port. You then should be able to use either the CraftsmanVit or rapid70 bullpup kit as is with out any kind of modification. If you still wanted a gauge you could remove the foster fill assemble and install the HUMA gauge and fill assemble for the Marauder. You have to use a fill probe but that’s not the end of the world.
edit
sorry I forgot that the SAM has a Picatinny breech and that the CraftsmanVit and Rapid70 scope rails attach to the dovetail breech. If that detail can be overcome it might work then.