At a guess I would say that these engine mounts are to help those people with tuning issues. Apparantly John Hazlewood had been running his engine upright at the start of this season, as he couldn't get the engine on tune due to the angle. (This is why in the pictures of the first SRS, Jon had his hand over the engine).
Only other reason I can think of is some engines may not fit properly (like the carb may not open fully) but I don't really know.
I have a Hyper 9, but it's the electric one, so my experiences with the car can't really shed any light on this.
Thinner centre shafts would be needed, as the stock engine mounts sit under the driveshafts, so if thatb side of the engine rises, something would have to give so they don't rub.
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