I've never sinewed a longbow, but I have asked several people that have a great deal more experience how well it would work. The concensus is that you shouldn't waste the sinew on longer bows. On longer bows the limb doesn't get a deep enough bend to really "load" the sinew and all it does is add weight to the limb and reduce cast.
The rule of thumb I was given for stiff handle bows was to double the draw length and add 10% (example: [26" x 2] + 5.2" = 57.2") Anything shorter than that will improve with sinew, everything above that will suffer from the treatment. For bend in the handle, just double the draw length without adding the 10% (example: 26 x 2 = 52" ).
Your mileage may vary, subject to state and local taxes, batteries not included.
