Here are some more photos of the Hawken Shop Hawken that Ressel had custom built and sold through his shop (top rifle) with an example of a Hawken built from one of Art Ressel's kits (bottom rifle).
Notice the variation in the snail of the breech plug. The kit built snail is "as cast" while the custom built rifle has a snail that has been filed in the concave shape typical of late Hawken rifles.
Also the kit built rifle has a lock Art used later that some say may have been made in India. Note the three screws showing behind the hammer. The middle one forms a pin that the sear pivots on. The top is sear spring screw and bottom screw is a bridle screw. This may be an English design, but these are the only contemporary locks I've seen it on.
A little off topic but still related, below is a picture of the lock area of a rifle that sold at auction sometime back that was represented as an original, but had a number of suspicious features. The most obvious is the hammer and lock. I don't think it fooled the serious collectors because IIRC it sold for a low price relative to original Hawken rifles, but still high for a contemporary.