I have a 70 roadster. I'm not sure about how the side cover was secured from the factory because mine seemed poorly fastened when I bought the bike 40 years ago, having just a bolt and nylock nut loosely fastening it. On the right sidecover I had a Dzeus fastener which went through the plate on the frame and fastened on the arm of the sidecover. The Dzeus clip acted as it's own stand off on the right side to locate the front of the sidecover. On the left side I had a bolt in it's place and the holes on the left side weren't wide enough for a similar Dzeus clip set up on that side. For many years I just used the bolt that I had and slid a length of rubber tubing over that bolt to work as a stand off, so I could tension the bolt and adjust position of the sidecover.
Some years later, I decided to drill out the existing hole in the plate on the left side so I could use the same Dzeus fastener which is used on the right side. I also had to rivet the Dzeus wire over the hole in the arm of the sidecover which was previously used for the bolt. I like that both sidecovers are quick disconect mounted. (although they may not be the way the bike was in it's stock configuration)
*Prior to mounting an interstate tank, I could unclip the Dzeus fasteners on either sidecover and have access to the battery compartment and oil tank area from either side of the bike very quickly and button it back up in a few seconds. The interstate tank I mounted doesn't give me enough room for the arm of the sidecover to pass the larger tank witnhout lifting the tank up slightly, so the Dzeus modification on the left side is no longer operating as conveniently as before, but it still is a simple solution albiet not stock...
