Nice looking machine; I had a new blue ’77 Electra Glide. 1977 was the first year for the “Comfort Flex” seat; what a monstrosity. I believe it was around 1982 when the frame mounted seat was introduced; frame mount conversions were very popular as I remember. Funny, but it’s kind of nice to see one that hasn’t been converted. It looks like your machine may have been painted; the color looks correct (from here) but in ’77 the fairing and bags were Birch White.
I have to chuckle looking at your mirrors. These mirror heads were famous for coming loose and rotating on the stem. The head is fastened to the stem with a ¼ x 20 set screw with a 1/8” allen socket head; this coincidently is the same part number for the fastener used with the earlier front axle caps (ask Spiderman).

One method that worked pretty well to keep the heads in place was to drill a shallow countersink in the stem with a 5/32” drill bit; even then the heads would work loose; I wonder how a “dab” of RTV would work in that application.
Prior to 1982, H-D didn’t have a large tour pack available, so large aftermarket tour-pac’s were common; although I don’t recall ever seeing one quite like yours. The mufflers are OEM and I believe that the extensions are an H-D accessory; although a number of vendors made them. The passenger backrest is an aftermarket offering; Ray-Cad maybe. The OE timer cover has been relocated to cover the slot for the OE passenger foot-peg mount. The side cover around the battery is an accessory; the set came with left and right covers; the cover under the seat is also an add-on. The passenger footboards were a popular aftermarket accessory; I have the same set on my ’78. Kromette gas cap covers; it doesn’t get any better than this; in a crash I understand that it was not unheard of to catch your “privates” on the cap cover as you were being ejected; now that would make your eyes water.

Great looking FLH, tompen.
djkak