doc F and Jim T,
You are 2/3s correct. Pica did acquire the rights to produce the Dave Platt Waco YMF kits under the Pica name but the kits were in 1/5th (72" ws) and 1/6th (60" ws) scale. Neither Platt nor Pica produced a kit in 1/4 scale to the best of my knowledge. Pica did redraw the 1/5th plans (twice) with Mort Tanger as the designer and Joe Tanger for the plans both times. The Pica 1/6th plans have Joe Hancock as the designer and Joe Tanger for the plans. Dave Platt was omitted from any credit with the Pica kits. The credits on the Platt plans show Joe Hancock as the designer and Dave Platt for the plans.
The kits appear to be identical between Platt and Pica as far as the wood parts. The plastic cowls I understand are made of different plastics but fiberglass cowls are available for both the YMF and UMF from Stans - AeroFiberTech
http://www.aerofibertech.com/products.html .
The second version of the Pica plans (1990) corrected the tail wheel location and left some additional info off that was on the early plans (no date). The AMA has the 1990 plans and templates (thanks to Bill) and be sure to ask for the templates when you order the plans. The early plans can be downloaded from the House of Moy site
http://www.houseofmoy.com/waco/ .
Doc - If you could post a picture of the kit box with the label it would help.
It seems that Platt started the confusion between the UMF and YMF by calling his kit a YMF but having the instructions for the cowl create a UMF (paired bumps for a Continental engine = UMF, equally spaced bump for a Jacobs engine = YMF). It seems that there were a couple of different production runs of the 1/5th with different UMFs on the box top; one was red/white and the other blue. The 1/6th I believe had only one box top. I have a 1/6th Platt kit with a Blue UMF with Yellow trim on the top.
Bill has more info on the box top illustrations and production runs.
For a ΒΌ scale YMF you have the options of the Pepino plans (not recommended due to inaccuracies in layout) or the Barth kit available thru Proctor. Give them a little time and AMR will have a couple Wacos in 27%.