I saw a side mount on a Remington Model 8 Friday. It had been soldered on, but I understand, from the owner/collector, that they also made ones you drill, tap, and screw down. Having seen this thread, I asked it he knew anyone who sold the mounts and he didn't, unfortunately.

The guy who had it had numerous Remington 8s, including some (quite a few, actually) very rare ones and an FBI model, which he had with him and did not have a mount on it. Not my cup of tea, but it's an interesting rifle.