Well, we're making some progress thanks to some friends across the pond.

I've determined the rear screws are 6BA cheese-head screws, just less than a third of an inch (0.305") long (so 6ba 3/8" screws will work), while the front screws are 6x48 SM7 (large cheese-head) screws 1/4" long. (6x48 Cap screw 1/4" long will have to work)

Now to find some of each!