An old system
There should be some sort of alignment dowels or holes noted with each rib. The number 1 and the 12 on the plans ought to indicate where these are at. Sand each rib to shape and drill in the alignment holes into rib 1 and 12 rib for a dowel, there should be some noticible position and washout.
Separate the two again and accurately drill the alignment holes into ten pieces of rough wood. Then laminate them all together again with rib 1 at one end and rib 12 at the other. Carefully sand all ribs to the shape of the larger, then begin to taper them to the smaller. You then result in a full set of tapered ribs. Use a wood rasp or file to cut in the notches for the spars. Kepp them all tightly bound together until finished too.
Wm.