Good points Jen. I don't have the engine in hand yet so I can't answer the question. I have not been able to find much on the internet on the "Royal 40" or 46 size engines other than postings on RCU with very few pictures or else where with very little detail.

I do recall advertisements in the model magazines from years past but don't ever recall making the connection as to the different crankcase styles.

I should have it in a couple of days and will follow up then.

cheers, Graham in Embrun near Ottawa Canada