I rescued one of my sandcasts from a breaker as basically just the motor and frame.  The frame is definitely set up as a CR.  It could be somebody's pretty well done mod of a standard CB750, but some of the little tabs and nibs are different from both my earlier CB750 sandcast (frame# about 600 units earlier) and my 10/69 diecast (frame# about 3500 units later).  Those aren't the sort of things I'd imagine somebody changing in building their own CR, and has me wondering if this could be an original factory bike.  Doubtful, but some aren't accounted for.

The frame number starts with the usual CB750-1005xxx.  Did the factory CRs use the same numbering scheme for the frame?  Or no numbers?

The engine number also looks normal, CB750E-1005xxx, where xxx is about -100 units different from the frame.  Is there anything in the engine that would easily identify it as being CR-spec that I could verify without digging *too* far into it?

My plan is to restore it as a CR since the frame is already set up that way, but it'd be extra-special if I could determine how much of it is the real deal.  

Mr. Bill