If your talking about the frame rail the sear sits in they might not have been punched out. If you remove the rail and look from the top where the body sits you should see three holes that don't go all the way through. The metal is thin and just tapping it with a punch or something will knock it out and then you can install the rear asa and or vert asa. The holes are not tapped you have to use the short headed allen screws from the top. Iirc they are 8/32 and I have found them in some of the larger hardware stores.