i haven't seen any fast rules for monster conversion. the feats and skills are really the only thing that mechanically changed.
BTW, the pyro dragon has my favorite dragon picture of all. but the one here from the Dragon magazine, not the weird one from Draconomicon
The breath weapons and major stats seem to be the same. Red dragon is 40' in each, ect.
Bulky Pyro dragon is actually 60' o_O
The abilities though; are sharply different.
I know Pathfinder has a Magma dragon but that doesn't really match the Pyro much aside from some appearance. When I read the entry I couldn't help thinking that it was some sort of lesser pyro dragon and that the pyro would be a stronger version of it.
In terms of converting to something more akin to the pathfinder dragons, I'd maybe take some abilities from the red and magma dragon.
The specific ones I would think would match the Pyro would be Fire Aura, Smoke Vision and Superheated
Honestly the fact that the Magma dragon DOESN'T have smoke vision seems downright bizzare since it has pretty much the same issues the red dragon has (BUUUUUUUURRRRRNNNN....oh...smoke....)
So retain breath attacks, retain spells and progression, retain all the stats, convert feats and skills to PF, add fire aura, smoke vision and possibly super headed. Add Planer dragon effect.
That unreasonable?