I decided just to add a fill hole at the right height. I just picked up a used HF mini-lathe for dirt cheap so I figured a weld-in thread bung would be a great first lathe project for me, rather than buy one online and wait for the shipping.
I started with just a 3" long, 2" OD chunk of steel, free from a friend. Then turned the OD and the face just enough to spin true.
Then reduced the total OD to 1.625" and drilled a pilot hole.
and bored it out to 59/64" or .921" for a 3/4" NPT plug
and beveled the face and necked down the OD of the rear.
finished it up and cut it off
and tapped the hole and finished with this. I ended up tapping the hole setting the plug a little deeper than I wanted, so I had to throw the bung back into the lathe and take some off the face. It was my first time using a tapered pipe tap.
The backside of the plug was supposed to be a little less than flush with the bung, so I ended up tapping the hole like 1/8" too deep. But again, it was my first time tapping a tapered pipe thread.
Tomorrow I will drill a hole in the cover and weld in the bung.