The first model year was 1982 for the Sidewinder, and they only came in Silver/Blue and Sierra Brown/Gold.
The frame date is irrelevant, and the 4 numbers stamped into the head badge is the actual day the complete bike came off the assembly line at the factory! In this case, yours is dated 2671, and that indicates is was built in late 81 for the 82 model year.
BUT, all that being said, given the condition of the bike, and the 79 dated cranks, I would say it is just a franken bike someone through together and painted sometime over its 40 years of existence!
If you want to fool yourself into thinking this is a factory paint job when given the documentation available for these, then I guess you can keep mind barfing.........LOL
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