Lyman regularly supplies such a sub-base with every #2 tang sight for Marlins - but I don't think Marbles does.
I have an extra Lyman/Marlin sub-base, but AFAIK the Marbles sight base's forward screw won't align with the forward D/T'd hole in the Lyman sub-base, AND Marbles doesn't sell an extra-long tang screw that's not only longer than issue to allow for the tang sight base, but even moreso to allow ANOTHER 1/4" for the sub-base.
BTW - The reason Lyman supplies the sub-base is that it's against Federal Law to D/T through (deface) the serial number.
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