I have built a penobscot and they are a lot of fun for sure. Not overly difficult, tiller each bow as you would normally, though the front bow only needs to bend a few inches. I put a layer of leather padding between the bows to keep it quiet and to prevent damage. One thing to keep in mind, once you mount the smaller bow it will slightly change the shape of the bend in the main bow. Because the design puts more of the main bow under compression, you might notice your tiller appear to "bow" out a bit more than normal, almost like a whip tiller in some ways. You will have to fine tune each limb once assembled(i prefer to tune the smaller bow so long as the large on is perfect on its own). Just my two cents, and best of luck!
