I honestly hope to know one of these days. I need to measure some stuff on the 2.2L heads, to verify they will in fact work. Things like rocker arm ratios, valve spring coil bind, rates, etc could all potentially be different, even if the cam looks like it will fit.
Plus, with the fact that the EJ22 heads have only ONE exhaust port, versus TWO on the EJ25 head, I would like to flow bench this and see what modifications, if any, will be necessary to my exhaust profile.
A few people have threatened to send me EJ22 heads to build up a killer EJ22 motor, but I have yet to see anything. Once I get them, I'll be more than happy to develop some parts for them.