I didn't tour the US in 1976 but was in Africa for two years in 77 and 78. I had what was a typical couple of bikes. One was a Peugeot from 76 and another was a Canadian Tyre branded bike bought in 72. Both used Mafac center pull brakes on 27" wheels (27 and 1/4 I believe) I don't think that 700cc was around yet except with tubular tires on a few serious race bikes. Don't take my word on that however.
I remember the wheels were steel chromed wheels which were on every bike of the day. How could one forget that with all the excitement trying to stop chrome plated wheels when wet. Aluminum came in the 80's I remember and wet braking hasn't been exciting since.
All of the bikes of the day were ten speed and double front cranks only. Triples were invented for the mountain bike crowd that came a decade later.
I remember the Peugeot had a simplex derailleur but don't know if that was common on non french bikes. The other thing I recall is that there were no sloping top tubes and frames were bought larger than is common today. A fist-full of seatpost was the common phrase in sizing thought to be right.
Oh ... no aero brakes, downtube (suicide) shifters, no indexing but only friction and the pedals were like the MKS silvan available today and had loose or retainer bearings that were traditionally oiled rather than greased (I could be wrong on that part - but that was how it was in my neck of the woods back then)
There was back then no such thing as an Ahead Stem. Only threaded quill stems, and just like my pedals, no press fitted cartridge bearings. I think cottered cranks were the norm back then too. Both of my bikes had them. Lastly only racers ever seemed to wear helmets and they were these leather padded strips type things. No such thing as a styrofoam helmet. All the people I saw had no helmets except a few enthusiasts really into cycling had cycling caps and once in a rare while a leather racing helmet, but you rarely saw that where I was riding in both countries. The dedicated guy would use wool jerseys and stuff things for quick access into those rear jersey pockets.
ahh, the good ol' days.