I've read where kits are available for removing the crossbolt safety on 39's and replacing it with what looks like another screw through the receiver. I sure don't want to buy what I think is a pre-crossbolt 39 and later find it was tricked. At what serial number did the crossbolt safety go into production on the 30's?

If you remove the crossbolt safety you will not have any other safety. The new hammers don't have the notch for a half cock. I would much rather get rid of the rebounding hammer than the crossbolt safety. They seem to be more accuraut without the rebounding hammer. That is an easy fix also. Don't know about any kits for the safety though.

After re-reading your question I see that it looks like you have found one that looks like it has been removed. It probably has. The hole is too big to have any screws in them so I would guess someone glued screw heads to cover the holes. Check to see if it has a half cock. If it does you will be alright.