Best thing to do is call 3 Rivers and ask.
If it's marked by bow length, re-mark it for string length.
The old "rule of thumb" is 4" shorter for recurves, 3" shorter for longbows.
ATA specs state 3" shorter, longbow or recurve (the bow is to be marked 3" shorter than the string master that puts it at proper brace regardless of what the bow physically measures).
Reality is either one is hit or miss. Although there is a standard, a lot of bowyers and manufacturers don't follow it. Even when they do, you may like your bow tuned outside the range you can twist up or let out a string.
Going by actual string length will save you a lot of time and frustration.
Also, even when going by string length, it can vary some depending on the material. For me, I go 1/2" shorter when I'm using BCY-X vs. Dynaflight '97 because the X has practically no stretch or creep once the twist is settled in.
Chad