original rear wheel size and sprockets

[reef5000]

Hi can you guys tell me what is the original size ofthe rear wheel on 74,cb,k.Also what is original sprocket ratio or how many teeth on front and back and what kind of chain will i have to look for if I want to by new one for these sprockets,Seem like that Iam clueless again.Thank you for your answers

[Re-run]

The original on a 74 was 18/48 but that ration is quite poor and loads the engine and can actually get worse mpg. Switch it to a 17/48 instead.
The rear wheel is a 18 inch rim. The metric tire size would be 120/90 - 18.