Mechanically nothing as far as I can tell. It seems to be all about the shift from Euro 3 to Euro 4, and the consequent change from Bosch Motronic 7.1 on the AQH to 7.1.1 on the AVP. With that comes secondary O2 sensors, individual control of the cam timing, and a warning light if secondary air isn't working. They changed the software and so also changed the engine code. BCS is the American version of the same thing, again mechanically the same but with different emissions specs. Cylinder heads, pistons, cams etc all the same so the difference in output is likely down to software.
Ironically, while the FL2 S8 got all the new Euro 4 gear, its still actually rated Euro 3 whereas the FL2 3.7 and 4.2 did achieve Euro 4. Luckily for British FL2 S8 owners though, DVLA class all the FL2 V8s as Euro 4
David - funnily enough I have a few items from that engine bung set from the two brand new engines I use
