I custom built a scope mount for my 513T.
I took a Weaver base, #63B, it was a flat bottom for a Marlin Lever action I think. Drilled a couple of extra holes to match the rear set in the barrel and put one dead center right at the front of the ejection port and installed a pin there for a recoil stop. I also used J.B. Weld to mold a curved base area around the mounting holes. It actually works real good for a "field base" but I haven't had time to see if it's solid enough for real target usage. I'm thinking it probably is, or maybe not. Good enough to win a turkey at the local gunclub, but maybe not good enough for real benchrest stuff. I have a 6-24 Tasco Target scope I use.
I might have some crappy pics if you're intrested, or maybe I can take some different ones this weekend.
I should have added that this base is deep enough that you can use the open sights with the scope removed but the base in place. This is normally what I do.