From what we can tell, Mosconi's run was 11 in the first rack, then 36 full racks of 14, then another 11 before missing. (37 break shots)
If someone were to run 526 starting with BIH on a break shot of choice, it would require 37 full racks plus another 8 balls. (38 break shots)
At the end of the old mosconi straight pool tutorial that's posted earlier in the thread at the end he's briefly interviewed and says his high run is 526 and that it took over 2.5 hours and that he's didn't miss but just stopped because he got tired. I'd hope he wouldn't straight lie but idk for sure how it ended either way.