Thunderguns71; The 68 4/v head is a 10 to 1 compression head yours is a 9 to 1 head and the valves are the same size. A 1.78 intake and a 1.45 exhast valve. I would say you'll gain about 25 hp.with after market intake ,carb and headers.Yes those heads are fine, you could go with a after market head to flow more. but the hp289 head is the same head just more compression or a smaller combustion chamber. I've done the same swap before and you will notice a heck of a differance in power. night and day.


Vegas