i was wondering if these heads will run right together.

3986339

458642

they came with an engine i have and im not sure of the specifics of them...all i know is that they dont match and the valve stems from 3986339 are too small a diameter for the 458642....the valve heads are the same size....are the combustion chambers different sizes and if they are, how big of a difference are the two from each other (and am i going to notice it running rough)