I'm with the reat... sink your pot deeper and get something else for an air grate.

Don't over-think the grate. A scap of 1/4" plate and a big drill bit will do. Or just weld (or even bend) a piece of light rebar or round stock into a grate. The only purpose is to let the ash fall while keeping the fuel in the pot.

Good luck,

Don

Consider just drilling a couple of 1/4 inch holes in the twyere and running a piece of 1/4 inch rod through the holes. See attached photo from BP0133. If you get access to a welder, look at BP0333 where a single 3/8 bolt is welded across the opening of the brake drum as a grate.

Nice forge, I can't add much to the comments, they have covered it pretty well.
You do need an ash dump in your piping, try a "T", a close nipple, and a cap.
remove the cap and ash dumps out the bottom!
Your block of steel looks like a weight from some scales. You could drill a hole in the stump, then cross drill side ways to meet the first hole, attach a chain to the bar
in the recessed side of the blockand an eyebolt to other end of the chain drop the chain down the hole, a nut and flat washer, and tighten it up!
It won't bounce around and the angle iron frame will keep from moving.