Hi. The Nylon 66, discontinued in 1989, was .22 LR only with a tube or box mag. The 10C, discontinued in 1978, same thing really, had a box mag or a tube, but could shoot Shorts, Longs or Long Rifles.
It seems that people who own a Nylon don't want to part with 'em. They don't appear on retail used gun racks or a gun shows very often.
"...unique Nylon stock..." Structural Zytel-101 developed by Dupont specfically for Remington.
The 552 Viper was discontinued in 1998. Only made for 5 years. No production numbers on Remington's site.
66 was tube fed. 77 was the mag fed semi auto version. The 10C was the same as a 77, but built specifically for dept store sales (Sears, Walmart, etc). I have both a 77 and a 10C, bought them for my kids. They are very light, makes them easier for the kids to tote. I've used them both on gophers a few times too though. Good guns, just be careful disassembling them, easy to lose bits. - dan