I can't say that I will greatly reevaluate his legacy, if his reach was shorter than I thought. It isn't going to change his record!
I see a 1 minute Reznick video complete with footage of atom bombs and cutscenes of the trenches of the Somme
Jack Dempsey, Ray Mercer, Max Schmeling, Mike Weaver and Sonny Liston are all listed as 6'1 on boxrec. Schmeling's reach listed as 76 Dempsey's listed as 77 Mercer's listed as 77 Weaver's listed as 78 Liston's 84 ....... yeah, Dempsey's could be an exaggeration.
78 inches of fistic dynamite....in nat Fleischer s book Jack dempsey...measurements of all dempseyx title bouts
I do not think we can know. On the one hand, he did not have an especially broad chest which adds to what we are really talking about-wingspan. Also being lean might make it appear longer than it was. OTOH he did seem to have fairly long arms, + his hands were disproportionately large. If you could compare him with someone whose height & skeletal strucrue seems similar, Tunney or his doppleganger Schmelling, that might be telling. He fought Tunney twice, but I dunno if the film gives any indication of this. How he & Schmelling looked so similar-that is the real mystery!
A reach of 77-78" seems like fantasy to me. His shoulders were not that broad, nor were his arms that long. 73-74" seems correct to me. There are several sources which say this.