[68c10owner]

With flat top pistons those heads usually give about 9.5:1 compression which is perfect. The smaller valves were great in engines like this. Once you start running more camshaft and winding it up higher you might see a increase in performance. Stock is 2.065/1.72 and the factory big valve heads use 2.19/1.72 on the closed chambers and 2.19/1.88 on the open chambers. You would possibly see a difference with some mild pocket porting and bowl work but stock they will perform well