When I had my AR A3 barrel cut down, my gunsmith turned the barrel down to .630" under the handguard, leaving the chamber, the section under the gas block (front sight bracket) and muzzle end as was. Similar to a GI A2 barrel profile, just a bit shorter. Not the same as what you will be doing to a Mini.
Parts nomenclature (in Numrich catalog): You have the "Gas Block, Top and Bottom" held together by four "Gas Block Screws." The "Piston (Gas Pipe)" protrudes back from the bottom gas block into the cylinder in the operating slide; what you call the 'nozzle'. All these are visible when assembled. There is also a "Gas Port Bushing" inside the bottom gas block between the gas port in the barrel and the Piston/Gas Pipe. Looks like you could make different ID gas port bushings to control operation although it would be a chore to change them out; unlike the regulator on a FAL. But I am not taking mine apart to see.
Knowledge comes from taking things apart. Wisdom comes from putting them back together.