We have a few GE P-39's at our field all with Robart retracts. I'm always amazed how they get retracts, fuel tank, linkage (engine & retract) fuel line etc. in that pointed front end. One P-39 at our field is a retract tail dragger (claims there were some made that way, no one argues). I fly the TF (red box) P-51B Mustang and if I recall, all the red box TF stand-off scales were smaller that their counterpart GE planes. My one recomender might be to install a 8 oz tank to free up some room. I always wanted to build a P-39 or 63 but was hoping someone would come out with a 80" wing span kit so the nose wouldn't be so congested. Good Luck!!!!