Thanks CP, propbuster; the engine is side mounted so that does make quite a bit of sense.

To be safe, I've already made another firewall with the engine mounted in the centre. A quick comparison suggests that the centrally mounted engine may actually be better aesthetically as the offset one had the muffler protruding out of the cowl by about 1/8". so I think I'll go with the engine in the centre.

Propbuster, in gratitude, if you're interested, think my LHS may have a kit left. Only problem is that it's in Singapore, and I have no idea how to get the kit to you. Alternatively, if you know how I could scan the plans with an A3 scanner, I could email you a copy. (I think the kit is way overbuilt, anyhow) I believe the Marutaka company is now defunct, so I don't think there'll be any infringement of intellectual property rights.