I built so many 65-75 GMs and you used whatever head bolts you had or could round up. They worked again and again. I later got some ARP 190,000 PSI IIRC in the specs but reusable too. I got them because the head was smaller instead of being 3/4 hex like factory and it was easier to get on the one by steering shaft when pulling head in chassis. But, hey, I took the hvac (factory air car) off the firewall and put sheet metal over it because it was in the way of pulling the last two pushrods out on pass side. I didn't need heat. That big engine warmed the windshield and firewall up in about 10 minutes. I used to drive it to college and back even when cold out about 9 miles away at 90 mph sometimes.