Overlin Single Fin Information?

I found this at a shop that does more soft tops and boardshorts than actual boards.  It was super cheap and as far as they knew it was called “collectable old surfboard”.  I found a little about Jim and Tom Overlin, but couldn’t find anything on this general shape.  It’s 6’8, single fin, about 20" wide, well over 3.5" thick and unfathomably heavy.  I’ve taken it out in thigh high slop and it catches small waves remarkably well, but I’m sure that’s not its intended use.  Anyone have any information about year, intended use, history, etc?  Thanks!

1973   plus/minus   one year.      Commercial leash cups hit the market in 1972 or 1973.      No, small waves were not the intended use.      Plenty of Pipline has been ridden on boards just like that.