Jack Sharkey was one of the most talented heavyweight champions of all time. His weakneses were entirely asociated with his unstable mentality. There was no shortcoming technicaly that I can see in any department.
The last time Sharkey weighed 185 lbs he was 22 years old. Chris Byrd was fighting as a middleweight at the same age. A peak Sharkey was around 195 to 205 lbs in an era when fighters did not do weights, and came in as light as possible for stamina. My guess is that he was basicaly about as big as Eddie Chambers.