Sorry Flashy, sometimes you just need to look past the stat sheet and actually evaluate a player based upon what you see. Nosek is bigger, more physically involved, actually drives the net, is more effective on the forecheck and much stronger along the boards than Sheahan. Hell, he even skates better than Riley (which isn't saying much). The only thing Riley has on him is his shot. More importantly, one of these two has continued to get better while the other has regressed mightily.
Nosek is no savior of this organization but is a better player than Riley and a better fit for a team in need of big centers.
They are essentially the same age, 1 has played hundreds of NHL games the other 17.
As far as their size, both are listed at the same height but Sheahan is about 20lbs heavier.
Comparing their play style is irrelevant since one is playing in the NHL vs the best players in the world and the other is playing in a developmental league with far inferior opposition. Nosek will not be very strong against the boards when he's got elite defenders checking him, nor will he be as willing to go to the front of the net when he starts getting abused by NHL defenceman.
Riley was a great player for Grand Rapids too, but managed to make the jump to the Wings in a season and a half, despite coming up into a roster that was infinitely more talented than the roster Nosek didn't crack last year.
The only argument that holds water when it comes to Nosek vs Sheahan is their cost relative to their production, and even that remains to be seen based on how Nosek does at the NHL level. (if he even makes it into the league)