That's the right approach, the .5176 dimension needs to be .500.
There is a previous post where the bolt circles and the angular displacement between the holes were discussed.
From memory (don't rely on this) it was something like 9" has a 10-3/8" bolt circle, 10" is 11-3/8" circle and 11" is on a 12-3/8" circle. All have a 32 degree angle between the two paired holes.
I found the post, the info above is correct.
https://www.fordbarn.com/forum/showthread.php?t=204069
Mart.