I mount my scopes onto my Contender carbine barrels with Stranton or Match Grade Machine scope bases & Leupold QRW quick detachable scope rings.
I use two basic options for rear sights when I remove the scope.
1) I mount an XS Sights low Weaver backup ghost ring sight onto the rear of the scope base I did have to grind off a slight bit on the bottom of the rear of the sight to clear the slelector on the hammer but it only took a couple of minutes to do I then just rubbed a little cold bluing on aand it was good as new.
2) Most of my barrels have the factory square notch rear sight mounted so I just mount my scopes bases behind the rear sight with high enough rings for the objective lense of the scope will clear the high point of the rear sight I use med height rings for 40mm scopes.
Here is an example of #2 this barrel is chambered in 375JDJ the second pic the barrel is chambered in 45-70 I'll have to dig around and see if I have a pic of the ghost ring sight mounted.
I sometimes just mount the rear sight in this case I removed the scope base and mounted the factory iron sight into the rear two holes of the barrel.
This is my son when he was 3 1/2 with his 16.5" barreled 22LR he's now turning 5 in less than 2 weeks so can handle the rifle a bit better.
This is one of the barrels I mount the ghost ring sight onto the rear of the base you can imagine just remove the scope and mount the ghost ring sight.
Here is a link to XS Sights
h ttp://xssights.com/index.php?nID=sights&cID=Sights&pID=sights&sID=rifle scroll down to the bottom of the page for the backup ghost ring sights.
If you are not looking at mounting a scope Skinner also makes a peep/ghost ring sight specifically for the Contenders
h ttp://www.skinnersights.com/thompson_center_19.html