(flew/fly very stably, so an F-104 PMC model should, with relatively little or possibly even no forward ballast, fly equally well.)

I respectfully disagree. I have built four F104 models and each one if them required a significant amount of ballast to get the CG where it needs to be. I used another modelers CP calculation that was derived from the cardboard cutout method. Each model flew very well. YMMV

__________________
Jim Filler
NARHAMS # 139
NAR CB - RCPC