Model 70 Classic rear sight|Winchester Rifles|Forum|Winchester Collector

I picked up a Model 70 with a missing rear sight. I think it is a Model 70 classic.

The sight mounting holes are 1.69 inches apart, which is farther than for a Williams rear sight.

Having seen photos of the classic with a longer rear sight base, I assume it is a classic.

I am in the UK. Do you know what type of rear sight I need and where I can order one?