'76 to sometime in early '78 had a smaller wiper motor and cover. Later '78 to '83 had a larger motor and cover. I'm sure someone will know the change date.
I have a '79 frame that was painted with bed liner after being scuffed with a grinder. It could be made to look good again, but it would need to be stripped or blasted and then it would need a light filler in a few spots to smooth it out before paint. It probably has some rust under the liner too. Yours for $75 + actual shipping.