Penn Jigmaster 500S. Pictures look like it's gotta "take-apart" side-plate thumb screw, only it's on the tail-plate side, along with 3 regular lookin screws on the circumference.
Also is the spool(reddish colored on the one I saw) plastic?
you are correct on the take apart, some of these came with the red anodized aluminum spool
I love an S, especially with red spool, they usually have steel mains and chrome plated innards. Only made for a couple years. Plates are delrin, not bakelite, and yes take-apart is in tailplate but other wise frame screw system is about the same.