These types of guns are not easy to do. As with Lehigh guns, there are a lot of details that you're just not going to get right by looking at the black and white photos in the picture books.
My observations: First, too much drop in the butt, and the comb angle is too steep. It WILL smack you in the cheekbone when shooting it. Yes, some later Berks guns do have butts with that much drop, but I cannot attest to their handling qualities...
Second, the cheekpiece is too well defined. Early (and some later) Berks cheekpieces are often not so sharply defined, and the wood around the cheekpiece sort of rises up to meet the cheekpiece edge. With these guns, always think rounded, and bulbous. Not "fat", but full...
I got to handle "gun 21" a few years ago, took notes and built a more-or-less copy of it. One thing I simply could not handle was the extremely hollowed out cheekpiece. VERY uncomfortable. The cheekpiece edge jabbed me hard in the chin. If the cheekpiece were flat, you'd be good to go. Some other Berks guns APPEAR to have flatter cheekpieces in the photos... but photos can be deceiving.
The nose of the comb (looking down from the top) gets very thin towards the front... just about the only part that is NOT bulbous!
The whole thing is very "sculptural". Flowing curves, in and out. The areas around the lock panels are a bit concave (it seems to have been a long lasting Berks trait). The fore end moulding gave me fits. Transitioning the bulbous relief carving around the lower rod pipe into the inset moulding on the bottom of the fore end was very difficult for me, and I still don't think I did it really right. The fore arm (ahead of the lock, where the hand goes) is very full and round, perhaps a bit thicker than on other types of guns, which can also be rather slab sided. Again, all very rounded and bulbous and sculptural. Probably my favorite types of longrifles.