The 2892 is a better movement. The issue on it though is that it is significantly thinner than the 2836/2824 which causes issues with stem alignment. I'm guessing with CNC options, anything is possible but it's a matter of cost effectiveness for one-off production.
The movement diameters are the same if I remember right (my reference material is not where I am)...but the thicknesses are around 1mm so then you run into problems of cannon pinion height, datewheel sinking, etc. If you buy an A21J version first, you'll have to cut off the dial feet and get dial dots to glue the dial onto the new movement. You'll have to source a new datewheel as the datewheel on the Asian may not work properly with the ETA...and then you'll need new hands.
If you want to go the Asian route first...best start with at least the Asian ETA clone, then at least datewheel and hands are fine...and odds are good the movement will be fine too. If it craps out, just get it fixed or get a gen 2836 and plop it in.