Those welded on nuts (the ones with the 4 weld nubs) look to be for sheet metal screws (pointed coarse thread). You'd have to get a size assortment to be sure which size is proper. Hard to tell from photos. Should be available at any hardware store. You could get round head slotted or phillips or hex head.
The ones on the left of your first photo look like they might be machine thread screws. Also available at a local hardware.


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.