Englishman, I don't weld the new floor plates on at all. I do it the same way it was done in London. I braze them on. I form the plates to fit the curve exactly and braze from the inside. It's very strong and I check my joint by putting them into soapy water about 1" deep. If they don't leek a drop in 5 minutes I know the joint is perfect.

93X64, I can't answer that question. I have never done one for a 375 2-1/2" but I would venture a guess that the mag box is the same and the feed lips are opened up. But it is still just a guess.