Simple and easy, buy whatever rear peep sight you want, but perhaps the cheapest and best for the money is the Williams receiver peep sight for the Buff Classic from H&R for about $18.00 (more if you buy it from Williams direct!!) Use one of the rear scope rail screw holes 9 the furthest back might be the best) and if the second hole does not match up have a gunsmith drill and tap one additional hole to match that sight. If you ever take the sight off and mount a scope rail the hole will be covered, if it shows you can put a plug screw in the hole or leave it as it is, no problem with that at all...good luck....<><....
"The Williams WGRS peep sight is available direct from H&R for $18.95(2005 price) part number R03019."