Interchangable engine parts 821 to 939.

Jul 2013
Does anybody know whether the heads are the same on a 939 and 821? Can the ecu from 821 be used on 939 engine and just flashed or something? My motor just took a crap and would like to use the opportunity to upgrade the power if possible. I've contemplated just buying the engine and ecu and dash board but that's going to be like 3-4k . Would like to just swap in the cylinder and pistons if that's possible? Anybody have any knowledge or experience they'd like to share? Much appreciated!
PS my vertical cam belt is shredded and once of the can gears feels jammed. Who knows what damage is done Im still tearing into the motor to gauge it.
Jan 2015
ECU is the same, 7SM, but another revision, so, not interchangeable.
939 has gear indicator in display, 821 has not.
939 ist Euro4, 821 is Euro3, mapping is more prohibited in Euro4 models by law so that Lambda/O2 regulation cannot be disabled as easy as on the Euro3 models.
I would stay with an 821 engine. I had both, 2 months even side by side.
Ok, 939 has a little more grunt, but 821 is more responible. top end power is quite the same, mine had the same topspeed.
I did drive both on track and on the same straight they reached the same topspeed.