We pretty well beat this to death and
thanks to all for the information. Especially the walking GM encyclopedia in SS. Still curious if the top and bottom screws differ, and if anyone believes this is an original bolt for the carrier. It may be for carrier under the bed. It's definitely a 67-72 serv 10-30 part.
http://shop.docrebuild.com/1955-1991...GM3991022.aspx