I just dug mine out of a container of ATF to have a look at it
The carb is an air bleed so the idle mixture screw is the small one running alongside the main needle and aimed at the little hole in front. The exhaust baffle was used before mufflers came into vogue to keep heat inside at idle but mine has a strap on Enya muffler.

The running in process for a cast iron piston is quite different than even for a ringed engine. A new cast iron piston is softer than the steel liner but after a little running the surface work hardens to become harder than the liner. A few heat cycles also makes the piston grow slightly in size so the two affects have to be juggled to get it run in properly. Instead of going through the whole process here, have a look at http://www3.telus.net/dieselcombat/breakin.htm which explains it all in detail.