That looks like, if I am not mistaken, a Raleigh Record. Made early 70's. What throws me off are the canti brakes. They must be a home frame welders effort.
Those DRs were an early effort by Simplex to work with reinforced plastic. Lightweight and breakthrough tech at the time but prone to sudden breakages now. Deterioration. Good idea to source some Suntour DRs.

Chain length depends on largest tooth count on front chainrings and cog on the back. Best to watch a vid on this. Simpler to understand by watching.

Where in NC are you ?