I'd say Kevin has this one pegged. Here's a screen shot from a Chevy Master Parts Book showing the exploded view of the earlier oil pump with the retaining bolt and associated hardware. Good catch Kevin!
~ Dan 1951 Chevy 3 window 3100 Follow this story in the DITY Gallery "My Grandpa Carl's Truck and How it Became Mine" 1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver) US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)
