When I got my truck, I found my vac advance can was seized up as well.

I found two different kinds in the junkyard. From the top the arm on one hooked left and back (mine), and the other hooked right and back. They were enough off from each other you'd have to do a lot of customizing to make the wrong one work.

Weirdly, the one I got in the junkyard does not have a stamp on it saying how much advance it provides.