Steel pan should weld up fine use a Mig or Tig and get everything as clean as possible. Concerns may be is the pinhole from damage or corrosion? If corrosion you may have more than just a pinhole once you strike an arc on it. One sure fire way to make a repair is make a small patch and weld over the hole. This should get you to good metal and prevent further opening of the already damaged area. Before you reinstall fill the pan with water and let it sit for a period of time to see if the repair took, any signs of weeping indicate you missed something.

1950 Chevrolet 3/4-Ton 3600
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