bozon,
The Mk IV would actually be enabled in all the arenas, perked in the EWA, probably perked in the MWA and free in the LWA. I would expect it would be free in the LWA because while it is still pretty fast, its critical altitude is a lot lower, its top speed is lower, its bomb load is only four 500lbers or four 250lbers and it is still unarmed. In the LWA I don't think it would be excessively survivable.
nrshida,
On the Mosquitoes powered by a single stage, two speed Merlin there was only room for five ejector stacks while keeping the aft most stack far enough from the leading edge of the wing and the radiator. The fifth and sixth cylinders on each side shared an ejector stack, the exhaust from the rear most cylinder being routed forward to merge with the exhaust from the cylinder immediately in front of it. You can see that clearly on this photo of KA114:
On two stage, two speed Merlins the larger supercharger pushed the engines further forward which created enough space between the engine and the wing for each cylinder to have its own ejector stack. You can see this on the two Mosquitoes in AH, the Mk VI has five ejector stacks and the Mk XVI has six ejector stacks and the nacelles are longer with the propellers being further forward.
