Classic/Antique Car Repair: 1928 Model A Ford Roadster, lebaron bonney, ford roadster

Question
Im trying to redo the top on a "28 roadster.  The irons are in good shape.  The three wood straight pieces are ordered, so also the top kit.  What do you do with the pockets on the curve of the irons where there needs to be a material that you can drive tacks into holding down the top material.  No one seems to have anything to fill those pockets with.  The original material looks something like masonite. I have the pockets empty and all rust treated but cant find anything to make the nailing surface with.
Suggestions I have received: silicone-too soft, hard as nails-too hard wont take nails, bed-liner material-perhaps if it can built up to 3/4 to one inch. Any ideas?

Answer
You got me on this one.  Those parts might be the steam bent pieces that come with new irons.  Not sure.  Call the outfit that you ordered the top kit from, or try calling LeBaron Bonney at 1 800 221 5408, or Snyders at 330 549 5313, or Bratton's at 301 829 9880, or Mac's at 800 777 0948.
You just need to find someone who has done this.  They will have the answer.  If you don't come up with the answer, get back to me and I will ask around.
Good luck
jack