Hey Mac.
Your photo puzzled me. �I went out to look at mine, then got more puzzled. �I scrolled back and looked at your #10 photo on Photobucket and it seemed as if the seat frame or the tank is mis-positioned or too large. �The tank looks just like mine. �
Is the seat frame a new repro? �I must warn you, I have 2A seats in a 3A Willys, but they bolted right up in the same holes. I haven't seen a 3A seat up close, and they are different than mine, but your seat frame seems too wide and maybe too long. �At the front, top, just before the curve down, I measured 20 1/2" from outside of tube to outside of tube. Is the rear wheel house a 2A? They are larger and that may push your seat too far forward.�
Here are a couple photos of mine. �


I know I'm not helping. �Perhaps a 3A seat owner will chime in.
Tim