I've noticed the MN base (repro) I have has two pins protruding from the bottom side. I guess they're for positioning the base? So You'd have to drill a little the receiver to accommodate these pins?
If this is a reproduction base as stated, I wouldn't have the first clue as what it entails. However, if you don't have the divets needed for the base, make sure you bought the correct A.M. part for your model. If it is the right base, did it come with any instructions by chance? Not being a smart A##, but some of the A.M. parts for my mosin came with very specific instructions as to what to do and how to follow and how many people it took to do it right. IF, it didn't, then proceed cautiously and safely. You can ruin it, but it is a mosin, so a dime a dozen.