That's a head-scratcher alright. Previous owner spray painted it black to cover white over-spray. I wanted to clean it up so I had the cleaning shop at work strip it for me. Well, the tech left it in the strip tank too long, and it etched the fins right off!
looks like a 3" core just by eyeballing it with custom end tanks. Measure the core, minus the end tanks, and search online for a match. You will have to have the end tanks fabbed but most shops should be able to take care of that no problem. If you need a recommendation, I know of an incredible fabricator in Birmingham, AL who can help you.
Looks like a cas dequick core. This is my setup and to me it looks like the same core. You should be able to find a shop to slide new fins in there...