I cant find any info on dan ryan bows so just looking for a broad range.
Not familiar with that bow, but if it's a d shape somewhere around 6 and a half inches won't be far off.
If its got a locator grip, you could probably go up to 6 3/4 - 7"
Try 6 3/8 and tweak it from there if need be. All my D bows are 6 1/8 to 6 1/2
6 3/4"-7 1/8", But I like a higher brace.