Jono if you want something just to test out, @Matt has made a no weld ammo box charcoal gasifier.
If you read it before I edit it in, I’m going to link some posts of the build. You’d have to make the charcoal and size it down but that’s as easy as burning wood in a barrel and snuffing it with the lid, then breaking it up with a shovel.
Since he made these videos he’s updated the nozzle design. Use this nozzle style in that build with the videos.
I want to say Matt has powered a 420cc Harbor Freight engine with this design but I can’t quite remember.