Super specimen Tom Sharkey, who went 25 rounds with the White Heavyweight Champ Jeffries, squares off with the Ronny Lyle of 1975, who just racked up two losses and surely lacks championship mettle. How many rounds does poor Lyle last under the relentless assault of the fantastic fighting machine? Does Sharkey go on to beat Ali a fortnight later? Foreman, too?
Since there is no real film of Sharkey in action (aside from his bout with Jeffries which is close to unwatchable) the question is unanswerable. However we do know experts from his time rated Sharkey very highly. Very tough, very durable, extremely well conditioned. Lyle was also a great contender from the 70's with his major issue being stamina and being relatively easy to outbox.
Ron Lyle = 6'3 220 pound modern heavyweight. Tom Sharkey = 170 to 180 pound fighter. I would have to go with Jack Sharkey. You know because even though their are weight classes for a reason, it doesn't matter when you put a fighter from back in the day against a modern sized fighter. Like for example even though Gene Tunney was a 6'0 170 pound fighter he would knock out Wladimr Klistchko the 6'6 240 pound fighter in one round. You know because he boxed back in the day. Rocky Marciano the 5'10 180 pound fighter who couldn't even beat 170 to 180 pound guys like Ted Lowry and Roland LaStarza would destroy 6'3 230 pound George Foreman and 6'5 240 pound Lennox Lewis because you know, he fought back in the day.
Tunney was a 190 pound hwt without Roids. Today's slow moving hwts without Roids would look very different in Tunneys or Sharkeys day. Tall and lanky.
Vitali looks far more natural than Wlad yet it was Vitali who was busted for roids before one of the Olympic Games so you can't totally tell just by looks.