If your mounts are supposed to have them, they act as spacers to raise the rear of the engine to line up with the gimbal bearing. The big fiber washer is to keep contact from occurring if the cushion mount were to slip and the engine drops down.
Additionally, they would dampen harmonics from the engine which could be transferred to the gimble housing. Since this housing is Al, I would be VERY wary of either fatigue cracking from high frequency,low amplitudes or catastrophic failure from low frequency/low instance elevated amplitudes leading to part failure. The prior is more likely.
The other posts above are also factors to keep the drive alignment correct...
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from low frequency/low instance elevated amplitudes leading to part failure. The prior is more likely. 
