Start with removing the head and just use the burnroom (maybe you need some M4 spacers to screw the burnroom tight).

Start te engine and run rich with a temperature of 80 to 90 Celcius.

After some tanks mount the head again and go on with the procedure on 80 to 90 Celcius.

With AAC engines we have several cooling heads and build it up to the right head and that is giving very good results.