Been there done that.
Get cheapo new stamped steel cover - weld (or have welded) in an O2 sensor bung and buy appropriate oil pan drain plug (18mm IIRC with sealing washer from your local Ace Hardware or elsewhere). If you want exact correct amount of rear end lube, drain and wipe out inside - then install cover and put in the correct amount of lube per vehicle specs. For future reference measure any difference between that level and your new drain plug hole using your finger, so you might want to have it welded just a touch high.

 

Got the cover replaced. Hammered a 13mm onto each and they came right out with an impact. Fill plug was a headache, it would not even come out when a bolt was welded onto it. I ended up removing the breather tube and filling it slowly through there.

 

Good work, looks great!

 

Good idea to use the vent tube! Congrats!