What about on a 1959 model?
The oldest catalog showing the Fistmele /brace is a 1961 catalog where there was a accent strip going through the riser of the Wing hunter and all I can find is “Recommended Fistmele” 91/2”-101/2”... Remember that some of those catalogs back then showed the Fistmele measurement being takin off the sight window belly side to string and some years are like many do here now and That is from the deepest part of grip or where your webbing between thumb and first finger is Seated in the grip to string.
As many have suggested and Kelly explained around 8” is a good starting point and move upward if need be .
Another thing you could check is how the string lays in the belly side of the string grooves and if the string is touching beyond that then it may not be enough and giving you a low brace .
If you twist too much then the string will be showing more of the filed groove under your string.
I seem to like it
Just laying near the end or about an 1/8” or 1/4” showing and seems to work for me but everyone is different and these are just starter points.
It would be nice if every Bowyer would write or include where a good starter point would be on the bows they make but there has been arguments about that in the past.
I’m just giving you the catalog recommendations on what I read .The other option folks used for many years is in this emoji guy