906 or 915 ?

IIRC the 915 was a 67 only 440 head, I can't remember if it had larger intake or exhaust valves or both. Although, I have a 426 wedge that appears to be a virgin, that has 915's on it, may have been swapped
If your plan is for a daily driver, I'd get unleaded valve seats installed in the 906's, or get a lead substitute to help cushion the valves