I looked in the G1MRA membership list, and see that you are a member, so I wondered if you had ever joined their MyFastForum site (which is now NOT affiliated with the Association) which now has pages and pages of experiences with assembling the RMN.
Lots of suggestions of filing and fixing things for a better fit, especially and angle file on the smokebox to slide it in.
Also this site might be of interest: http://www.britanniabuilder.com/aster.htm
David Leech, Delta, Canada
p.s. My RMN will stay in it's box until next year when I hope to find the time to build it.
p.p.s For some reason the PM system does not work,so trying this way!