I don't know why you would want to build a Royal spitfire as a control line airplane, keep your eye on eBay there's a guy in Indianapolis Indiana that has one completed and it set up as control line. A10CC gas engine is the equivalent of a 60 glow.
I suggest you go with a 15 CC. Also join the royal kits group on Facebook I'm the founder.
https://www.facebook.com/groups/170232020405624/