So you "ordered" a board of hickory... Where did you order it? A true bowyer, I hope? You mustn't order wood at lumberyards, because they have no clue how straight the grain must be. You must be able to see and select the wood yourself before buying wood at a lumberyard.
If you do get a straight grained board of hickory, it will be possible to make an English longbow from that. Hickory doesn't really like to have a narrow and thick profile such as in an ELB, and tends to take set in such designs. Your best bet would be to make the bow as wide as possible, while still be in the ELB category with 5/8 thickness to width ratio. You may want to trap the back (meaning that you create a trapezoid cross section by angling the sides of the bow, resulting in a belly that is wider than the back). Start with a width of 1 3/8" for the center 12", tapering to ½" nocks. Thickness tapering from 7/8" in the handle to 5/8" nocks. If possible, go slightly longer, say 72".
Remember these are just starting dimensions. Once you've carved the wood to these dimensions, you'll need to start floor tillering and carefully reduce the width and/or thickness to get a good tiller and end near your desired draw weight.
