A picture would be able to clear up a lot of questions but my guess that if it is indeed a 70's Cayo fifth wheel it is very rare. Avion/Cayo made a fifth wheel for a year or two in the late 80's and early 90's if fact there are a couple of threads on here where people are currently fixing them up. In general from what I know Cayo made motorhomes and truck slide in campers and Avion made the travel trailers. If you want some professional advice why not ask the source? Cayo still runs a shop in Michigan give them a call and maybe they can help.
Please report back here with what you find out. I for one would be very interested in a previously unknown model of a Avion/Cayo. Oh and Welcome to the forum!
1972 Avion V-25 Voyager
2010 Nissan Titan CC