Get a Lyman rear folding leaf sight. http://www.midwayusa.com/product/516...levates-to-445 This type of sight came standard on a Winchester Model 88 Lever gun I bought new back in 1972 and still own today. IMHO these are the best open rear sights that you can see and use. They make them in different heights so measure before you buy one, should you choose this type.

Dave