I had the same idea as you for the rear sight. Then I checked with H&R customer service and was told I could not get the factory rear base from them. My idea was to get that base and configure it with a "One Ragged Hole" sight blade. I still may get the ORG sight kit, but just leave the base where it is.
Here is the link for One Ragged Hole.
http://oneraggedhole.com/index.htmDo your shoulder a favor and put a Limbsaver on that 12ga. You will be glad you did. I have one on my Tracker I 12ga and the felt recoil is noticably less than the felt recoil on my Tracker I 20ga that only has a factory recoil pad on it. I was pleasantly surprised, to say the least.
I have even thought of filing a small "V" notch in the receiver, centered on top of the breech, to use as a sighting point and then adjusting the height of the front bead. A guy can come up with all sorts of ideas, problem is testing them all out.LOL
cookiemann