The Gen 2 M62 appeared on GM cars in 92 and ran from 92-93. Park Avenue, Bonneville and Riviera. This supercharger had no coating on the rotors and a 2.5" pulley stock and thermal coating on the exterior body of the charger.
The Gen 3 M62 replaced the Gen 2 for 94-95 years. This supercharger looked similar to the Gen 2 and had coating on the rotors. The coating on the rotors increased efficiency. There is external coating on the Gen 3 M62 as well as an external fin difference from the Gen 2, I forget which is which though.
The Gen 3 M90 took the M62'* place on the 3800 starting in 96 with the new motor design for the Series II. In 96 the supercharger body was coated with thermal coating like the 92-95 M62'* and had a vacuum tree near the throttle body end of the charger. 97 stayed the same except the exterior thermal coating was not present on the charger body. In 98 to current the vacuum tree was deleted and no thermal coating.
The Gen V M90 appeared on the scene in Grand Prix'* beginning in 2004, this redesigned M90 had a more efficient airflow and longer rotors than the Gen 3 causing it to run much cooler than it'* predecessor. The Gen V bolts right up to the LIM of a Gen 3 except for a slightly larger outlet opening. Different throttle body bolt patterns make an adapter plate necessary to swap from Gen 3 to Gen V.
The M designation is the amount of cubic inches of air per revolution that the charger moves. An M62 moves 62 ci of air per rev and an M90 moves 90 ci of air.
00 Regal GS: All kinds of cool stuff.