Measuring string length?

[akdd]

I had two recurve bows gave to me with out strings and I need to figure out how to measure them. One of them is a Howatt Deluxe Fifty Four it has a 58 with a 2 under that stamped in the sight window. I cannot find any other markings on it. Measuring from string groove to string groove following the back of the bow it measures 70 1/2". The other bow has no markings on it that I can find it measures 67 1/2" from string groove to string groove.
What length of string do I need for these bows?

[JRY309]

I measure from nock to nock following the belly,I'll put my tape on one nock and then straight to the other nock.I do this on my bows even if they are marked,when I make a string for them.I had three 64" longbows and everyone was a different length,within 3/4".