Thanks Jim, Ed, Don, and Ron. I appreciate the comments very much. Eric, you are completely correct. The Siler on the gun was a kit bought from TOW. I also happen to have a new small Siler (assembled) that I bought for another gun and that one is stamped with "C"s in circles so I guess it was actually made by Chambers. The kit has no markings. The tumbler on the kit is different without the deep depression for regulating a constant position of the sear at rest, half cock and full cock, and the notches are placed differently. The new Siler has plenty of clearance for the flint at half cock. Also, on the kit, the nose of the tumbler dropped 1/32" below the plate when the flintcock was at rest. I had to reshape it to prevent that, which was very easy to do. I will swap out the old tumbler. Thanks for the tip.
dave