I think you're getting a bit confused with the x flow and the valencia, which is a crossflow engine but not THE crossflow.
The crossflow as used in RWD is different to the "crossflow"(real name valencia) dimensionally, (most)parts do not interchange between the two, certainly heads and cams etc.
The reason why the valves are in a different order is because the firing order and cam are different between the two, the x flow is 1342 but the valencia is a 1243, the valencia is effectively a sqaushed up shortened x flow, made for FWD.
I've no doubt you could swap bits about like crank but there will also be a different block height most likely, so would need the bigger cc block to go with it otherwise with longer stroke pistons will be sitting on top of the block instead of flush with it.
tabetha