Re: 1977 6 HP evinrude Model number 6704 M Engine cover
'76-'79 6hp Evinrudes used a similar-shaped cover. The same cover was used a bit earlier on 6hp Johnson outboards, from around '70-up. You do have to watch out for the latch design, earlier Johnsons had a latch on the back of the cover, whereas all the later-models had a latch in the lower motor pan.
Here's a cheap Johnson cover on eBay, you could strip the decals, repaint, slap an inexpensive set of eBay Evinrude decals on it, & call it good:
