I have a set of Power Pack heads in the shop. My machinest tells me they need hardened seats. Running old heads with unleaded gas is problematic. The lead acted as a valve lubricant. Take away the lubricant and the valves eat their way into the soft cast iron. The fix is hardened seats. He quoted $30 each or $480 for the job. You can get a set of street replacement heads that flow better for that kind of money.

If anyone wants my Power Pack heads I'll take $100 for the pair.