Seat belts, side mirrors, windshield wipers and reverse lights were made mandatory in '66, but I'm sure some of the trucks made earlier in the year didn't have them yet. You can tell a '66 stepside rear fender by the indentations for the reverse lights.
Bear's right about seatbelts being an option prior to '66. Luckily my '66 replacement cab has them, because if I had used the '64, I'd have had to retrofit them.
I know this doesn't help much with your request, but if no one posts pics, I'll get some to ya tomorrow hopefully.
