The 915 heads were fitted with 1.74" exhaust valves when used in performance engines. For non performance engines they were 1.6" I think. If you have the smaller valves you could cut the seats and fit ther larger ones.
Top pic of head is to show difference between a good sated valve and the bottom shows the valve with no seat left, valve is right back into head.
So these are two different heads, the one with black valves is from a different motor.
What? Like we don't know what a stock valve looks like? Even I remember those from way back when.
Sorry Dave , you missunderstood, i took the pics!, and was just pointing out that they were 2 different heads, it was just to show Nick his valves compared to a valve from a head i have myself.