Good luck in the quest!
If the engine number is CB750E-1007414 or lower, it is a sandcast.
You sent me your cell number... will give you a shout soon... isn't much to see with my sand cast as it is a project... but you can come down and take a look if you like.
Btw, if the bike is a 1969 it is quite valuable even if it is die cast. The prices have gone nuts on the 69's (in my opinion).
Regards, John