Jelco Arm mass and cartridges

I was thinking about a Jelco SA 250 S arm, but noticed the effective mass at 20g seem high compared to others I have looked at. I believe the 750 is the same.

I understand the headshell to be about 12 g. If you buy a lighter headshell, do you subtract that difference in headshell weight from the effectice mass of the arm ?

I ask as it would seem many of the MM/MI cartridges I would try would be a miss match.

Any info on the cartridges and mass with the arm appreciated.

Thanks,
Wayne