In post #24 I noticed, that the Argosy has a lengthwise kink in the fuselage, probably at the level of the floor. The Fokker F-27 has the same kink. For the F27 it was meant to provide some protection against a belly landing, it contained a strong keel beam. Is it the same for the Argosy?
Having had the dubious pleasure of ferrying an F-27 which had suffered a belly landing, I can assure you it didn't offer any protection I could see. That was a case of undercarriage retraction after landing. Not a full higher-speed wheels-up.