That's an interesting question. I never saw one of them, but just assumed they were re-angled using 5/8" guides, like the Dunstall and other period big valve heads. On re-consideration, it seems more likely that they pulled unfinished heads out and machined them to take the 1/2" guides at the new angle. When they did the 850 style big valve heads for the short stroke 750, they didn't use a larger guide, but kept the 5/8" 850 guide, which means they pulled them off the line before the guide holes were bored, and machined them to suit. Folks who converted finished 850 heads to the big valve configuration had to go with even larger diameter guides to allow re-angling the intakes. That's why Steve Maney eventually started converting 750 heads to the 850 bolt pattern, so he could do the big valve conversion and only have to go up to the 5/8" guides.
Anyone out there know the answer to Seeley920's question?