Tom,
In the 1964 catalog the recommended fistmele (brace) was at 9 -3/4” which seems like a lot and I believe I have mine at 81/4 “ to 81/2” but can’t remember off top of my head because I haven’t shot them in a year or so.
The design didn’t change a whole lot from the Hi speed for a few years that I can tell other then the sight widow and some of the tip width but I think that was due to which bowyer was working on that particular bow when it was being shaped from what I gather from Larry Hatfield.
The grips are very deep on some and you may notice a few have a higher heal but I believe if memory serves me correctly I read that would of been a custom request .
Try around 81/4” and work your way up with a few twists and see how your arrows fly .
I’ve noticed a lot of the catalogs show some older 60 model year bows have a higher brace then in today’s bows but most are just recommended as a starting point and it’s up to some to find that “Sweet “ spot where they can tune an arrow to their liking.
Keefers