My 1975 Argosy 26 is a little different setup, but I literally just removed the refrigerator (and everything else) a couple of weeks ago. Photos of the Demo can be found here:
The fridge related photos are towards the back of the album.
Mine had floor screws, and a 'Bracket (wide bent metal strip)' that was attached to the frame, as can be seen in these photos:
And of course, it had propane hookups that needed to be disconnected.
Also, I'm pretty sure mine had been serviced since someone wrote profanity in the soot behind the fridge :-)
I'm not sure any of this will apply to your Argosy, but I thought the photos might help give you an idea of the methods they used for attaching fridges to the Argosy's back in the day.