I think that's the same model pictured in the first post here, and several others in this very thorough thread about the Fenwick blanks of the era.
viewtopic.php?p=124703#p124703 To me, that blank builds into one of best fiberglass "river rods" as I call them, whether compared to others of its time, or similar 'glass configurations today. I have a couple others I like
slightly better, but I don't miss them when fishing the Fenwick,
Hobbyists and small-shop builders made them into fine rods according the user's taste and hardware preferences. In the mid 1970s, many would have been fitted with aluminum Sizematic ferrules. About that time they started to come with a fiberglass sleeve ferrule fitted at the factory as well. Would be curious what ferrule type yours was built with.
You have an excellent rod. Nevertheless, magic is right on with his estimate. Rods built from blanks are typically worth what one might pay for a new old stock blank, maybe a little more if the build is appealing for its hardware or cosmetics, maybe less because they take work to rebuild to the new owner's liking.
Maybe you would enjoy fishing it; that won't substantially change its modest value, and it won't owe you anything for the enjoyment it provides.