i'll probably get sht down in flames here, but i have 2 the same and did alot of net searching.
i'd say late 80/pre march 81Motomag. 1 as the first number to appear after the f is usually the last number of the year, 1981. the stickers with the black background and gold writing, red band/decals at back and the larger 'winners choice' sticker on downtube. i need these decals for my next build and should be available soon.
these were also on some after march 81 but the rear dropouts changed to kinked ones with holes.
for me pre march 81 Mongeese are the only ones im into.
good score, will clean up a treat.