Personally, I'd start it off at 60". That's only a little longer than 56", really. Just leave the sinew short of the tips, say, 6" from the nocks. There's no real use for putting sinew all the way over the tips, especially if you use a good glue and/or snake skins. Heck, wrappings even work. That way, if it comes in too light or you just want it shorter later, you can simply knock the tips off and cut new nocks, no worrying about sinew
. And with sinew and Osage, you might be able to go down as short as 48-52" with a bendy handle later if you wanted.