Plenty of old-school mesa guys were qualified on the 200...as long as they stay current on the 700/900 and the 200 is still on the certificate they should be good for 121 ops. While you had to get an initial checkout on each sub-type there was never any ongoing currency requirement for the sub-types...current on one, current on all unless their opspec says otherwise.

For part 91 it's a common type, all you need is the type and GTG.