Otto, I think you meant 5/16" bolts, which have a 1/2" hex head. 1/4" bolts or even #10 screws would be plenty to hold them in place.

Another possible source for original style clips is Restoration Specialties. They have a ton of different style similar clips. LINK

Or you could use the plastic "Christmas tree" style push on fasteners. Or split rivets if you want to stay with steel.

Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.