There’s the Elevated Kinetic Energy Test Bed, that looks like it is using a M551 chassis, which could be neat. I think it uses the same, or similar gun, as the HSTV-L and RDF/LT in the game. So perhaps a bit higher BR than what you were looking for.
The XM551 with the M68 105mm gun would be my top wish for a Sheridan variant. It would be a huge upgrade in firepower for that poor vehicle.
I’m definitely not a fan of the standard version’s 152mm HEAT-rounds. And don’t get me started on those nose-diving missiles… So getting an actually potent and familiar gun would be a huge upgrade and hopefully fill a gap.