The M3/M3A1, M16, and M3/T48 have the same armor, same engine, and same chassis.
If HTC wanted to, they could easily fit them all into the same M3 selection but pick and choose which variant you want. The M3 and the M3/T48 are different only in mission capabilities, not chassis, armor, or engine. I'm sure the M16 and M3 could be viewed just the same.