Treat the Royal as if it were a OS 46SF and you will be fine.
The engine is ABC and not ABN like some of the OS engines
The last MECOA 46's are the same as the last Royal 46's
http://www.mecoa.com/mecoa/46/4603.htm
http://www.mecoa.com/mecoa/guide.htm
https://shop.mecoa.com/shopdisplayproducts.asp?id=146 Parts list