Adding a drain plug 727

DON'T weld a nut on the inside of the pan. Think about it; picture it in your head. The nut will act as a dam and not allow you to drain all the fluid (and funky sludge) out. Get a bung fitting and weld it to the outside of the pan, being careful not to warp it- it's only thin sheetmetal. Or, by the time you buy the bung & plug and weld it all up and straighten it out, you could have just bought the pan with a plug...