Lionel made the 2359 Boston and Maine GP-9 in 1961 and 62. There are no variations of this loco.
As a side note, the difference between a GP-7 and a GP-9 is the addition of a dynamic brake to the top of the cab.
In 1965 the B&M diesel loco reappeared in the catalog as the 2346 loco. The 2346 Boston and Maine GP-9 was cataloged in 1965 and 66.
Both versions are equally available today and neither commands a premium.