Order the plans from Model Airplane News and stretch the mains per that version, especially if you are flying off a grass field. Even if you have a paved runway the minimal prop clearance could cause prop strikes. My first Duellist was the Pica kit and I had way too many prop strikes.
My current Duellist is the MAN plans version Mk II and now that I am flying off grass am gratefull for the longer legs! If you stick with the gear per plans zero the incidence on the engine nacelle to the wing that will give you just a little more prop clearance.
Buy a Twinstar and throw a pair of FX 25s in it while you are building the Duellist. I went through 2 Twinstars and had finished "White Lightning" before I flew my Duellist and was glad I had some twin experience. All of my twins are or have been great flying planes when both engines are running but if you don't react correctly when you do lose an engine (I'm guilty of that), grab a bag and take it home.
There is plenty of twin advice here and on other sites by flyers with much more experience than me but that is my contribution. I'd be happy to answer any questions about building the Duellist. Drop me a note anytime.
Pictures below, first and second Twinstar, White Lightning (Tower Uproar), first Duellist (Pica kit), second Duellist (same wing, new fuse built from plans), second Duellist had a bad day....current Duellist