I have had this enlarger in storage for let's face it, decades. I am now moving and am looking to give it away, but need to determine if it even works. I have the base/structure assembled and the head/condenser was really well packed and covered.... the motor works, but for the life of me I can't figure out how to attach the head assembly to the structure. I may be missing a part, and there is a mystery broken piece (circled in red) [Note that the bolt is just propping up the broken piece]. My memory is the flat thing sticking out of the head unit slides into something, but I don't see anything appropriate for that. Any ideas what I am missing? Thanks.