Welcome to the forums!
Here is a link that will help a bit with identification, if you are sure it's not a 1967
, then it looks like you may need to look for a manual from 1970 for more information. Dr. G on this site is VERY helpful, he is great at returning emails. I am sure you will find what you need here or at least how to get what you need.
Avion Travelcade Club Travel Former member Fifth Wheel Fleetwood Trailer Cayo RV Repairs Interesting Email Winona LakeIndiana Unit
Also, post some photos. That will help everyone weighing-in with their opinions as to value. Condition is huge - how much is original and how much is missing? There are one or two other threads on here regarding the Avion Truck Campers and their restoration. That will help you with photo references.
Again, welcome and good luck - Avions are great!