Ok, I have got all my tools up and running and done some final calculations.
Here is what I come up with:
All 66" NTN
16" riser
these are total stack including glass measured at the thickest (butt) end of the laminations.
55# bow with reflex at 1.25 inch wide = total stack of .425
55# bow flat at 1.25 inch wide = total stack of .438
55# bow reflex at 1.125 inch wide = total stack of .438
55# bow flat at 1.125 inch wide = total stack of .451
To make any of the above a 50# bow, reduce the applicable stack by .014
While Bob's numbers differ somewhat from mine, don't discount them entirely. Think it through.
As you can see by the .014 figure to reduce 5# of weight, it does not take very much to effect the strength of the limb.
Choice of wood cores may have some effect but contrary to the anecdotal observations of many archers and even bowyers, I don't think you will find much difference in the draw weights of various woods. Heavier core woods may result in slightly slower shooting bows, but not by very much.
What is your source of instructions on the actual build?