a set of rings should attach directly to the top. If the forward ring needs to be positioned further forward, either a set of riser blocks (using the rear block on the front and overhanging) or a set of Hawke extension rings from opticsplanet.com will work great.
Early manufactured rifles did not have the scope rail. I have a factory rail from anscutz that I could sell. Send me a pm and post here so i can see if you are interested.