71 was the first year for Argosy but that one sounds like a lot of time and money needed to get it camp ready. That year did not have gray tank so one needs to be added. I just finished a restoration on a 28' 1960
that had most everything with it and it took 3 years to complete. Lucky I have 2 finished trailers to use.
You should look for a trailer you can use as is, then get one to work on, it makes it a lot easier to look at all the work needed, when you can go camping right away.
I would think you would have more in it then it could be worth so a starting price should be very low like $500 - $1000 at most.