Attachment 108847
Not the best image for explaining my point... But I've looked over the hull and the holes are all there for Bren mounts, antenna mounts, rifle rubber rests etc, so I'm concluding that the engine cover must be a donor from a UK Mortar Carrier.
If anyone has a Mortar Carrier and wants to trade for a standard Mk1* engine cover let me know, before I start making holes in it. I'd rather not modify it, but want to return mine to standard configuration so will need to put the missing holes in it.