[Buster_Dee]

"The question now remains though, which 2 are used for inlet, the outer 2 :?
[edit] Ok, by looking at the screenshots in this thread again, I think we can say the outer two run in sync."

The link below seems to be a 2-cylinder MWM version of the 6-cylinder MWM used in Type IIs. Notice that the center rocker is not moving. It's not even really a rocker arm--more of a half rocker. There's also something odd about its spring arrangment: it doesn't actually align with the other springs, but more under the "cup" between the other two rockers. Look carefully at the other photos in this thread, and you'll notice they actually agree with the clip (Half a rocker. Springs are not like the others).

After some more research, I think it is part of a cam-operated pneumatic starter. The push rods open an air valve to push each piston down in the correct order for starting. The push rods are probably driven by the same cam that drives the valves (maybe even by the same intake lobes), but the "air" push rods are held off the lobes during running.

I think you could save some polys, and certainly save some animation work (at least during normal running). I would still go with your current solution until it is definitively disproven.

Thanks for this by the way.