Anthony,

I have access to about a dozen Wacos, but not a YMF. YMF Classic NC 14081 did come to the 2007 Fly In and I did get a bunch of pictures, but not measurements. I have used a UBF-2, NC 2091K to get some reference #s for the screw spacing but not the rivet spacing on a YMF bump cowl as shown below. The UBF has a Ring Cowl.

P1 Screws at the hinge line of the front cockpit door, UBF-2, NC 2091K
P2 Screws and fasteners in front of the forward Cabane strut, UBF-2 NC 2091K
P3 Cowl detail on 1987 YMF Classic, NC 14081. The 1930s YMF cowls were similar to the UBF-7 Bump cowls in P4.
P4 Cowl on UPF-7, NC 39727. Note different fastening method and how the bumps are fashioned