I don't like the cotter pin; it doesn't have the same side-load strength as the proper clip. When you go to a hardware store to get new steering column bolts, get another linkage clip.
I don't know that bolt size off the top of my head, but I suspect they are metric. Try some other small bolts in the holes, such as one from the gas pedal, to see what fits. One of the column bolts had a sheet metal thread stud on it, but I don't remember what for without looking. It may be to hold the small rubber boot in place that sits at the base of the column.
Dixie Restoration Depot sells the steering column-to-firewall gasket.
It looks like your master cylinder is weeping inside the firewall.
I don't know that bolt size off the top of my head, but I suspect they are metric. Try some other small bolts in the holes, such as one from the gas pedal, to see what fits. One of the column bolts had a sheet metal thread stud on it, but I don't remember what for without looking. It may be to hold the small rubber boot in place that sits at the base of the column.
Dixie Restoration Depot sells the steering column-to-firewall gasket.
It looks like your master cylinder is weeping inside the firewall.