Here are the nipples for the drains on inner primaries, HD started using these in late 36, these are made out of mild steel and weld really easily.
Here are the 20 inner primaries that I am working on. We have tried all of the different inner primaries, there are probably four different companies on the market, and these are the ones that fit the best. They just need a couple details to make them use able.
In this pic you can see the nipple that I welded in, I also welded up the hole that was punched in for a drain. This is a cool fix.
20x! Now I have to make and spot weld the splash guards on. I think I might try making a forming die to make another modification too.