Hi. There's a drawing of a longbow I made recently on our club website at
http://www.scfa.org.uk/longbow.pdf . This shows the dimensions for roughing out your blank. Shaping and tillering then need to be done slowly using something like a block plane and flat bottomed spoke shave.
I've tried these dimensions using Ash and Pau Amarillo (like lemonwood). Both shoot well. Both bows are 40lb draw at 27", but I had to remove considerably more wood from the Pau Amarillo blank.
Please share your progress with us.
Regards, Dave