64 Classic 770

I found this below on the Internet but was wondering about the other stuff. My 660 originally had an AMC 15 differential and 9" brakes. 

'The bread and butter Rambler was the 660 (135,000 sales), a more posh version with carpets, armrests, Captive Air tires on wagons, and a few minor goodies. The Rambler 770 added as standard a clock, padded dash and visors, full wheel covers, and foam seats.'

770, 660 and so forth were just trim levels ( outside chrome, inside upholstery ), had nothing to do with mechanical equipment.
You could get a 770 with six or V8.
You could order heavy duty brakes with a 6 also, on a AMC 15 rear, but you automatically got bigger brakes along with a AMC 20 rear if you ordered a V8.

I don't think AMC ever put a AMC 15 rearend behind a V8.

67 and later,in senior AMCs, you got a AMC 20 rear no matter what engine the car had.

They did the AMC 20 standard starting in 65 on all the TT cars, 6 and 8. Before that you could have either depending on the engine, or perhaps fleet cars?

I have an AMC 20 that I believe is 3:15 gearset with Twingrip. I know it is twingrip, just not positive on gear ratio. I'm going to open that case and check it out, It will be for sale, parts or whole. It even has a fairly nice twingrip circle tag on the fill plug. Came out of a 65 990H car.

The AMC 15 was only used with 195.6 and 199 powered cars. All other big cars used the AMC 20, six or V-8. There were only a few 1966 big cars with the 199, and it was a fleet only option. I've never seen one -- I doubt many fleet cars were ordered with the small six, and those that were got hard use and were worn quickly, and were most likely base models that seldom get saved.

All sixes in the American (and other small cars -- Hornet/Gremlin/Javelin/Pacer/Concord/Spirit/Eagle) used the AMC 15. Only V-8 cars got the AMC 20, though it may have been a HD Fleet option.