Here are some pics of the frame after I took the skin off my Greenland kayak, based on fig. 208 of Adney and Chapelle's book The Bark Canoes and Skin Boats of North America. I took a block plane and shaved off any residual polyurethane where the skin adhered to the gunwales and chine stringers.
Pulling the skin off took some big chunks off the keelson, so I ended up completely replacing the keelson. First I cut all the lashings which held the keelson to the ribs. Then I cut the keelson off the stems by sawing the pegs in the joint between the keelson and the stems.
I happened to have a piece of cedar ready that was the perfect dimensions for a new keelson. It was left over from the build two years ago and I had been using it as a batten for lofting my sailboat. I attached the new keelson by extending the notch in the bow and stern stems and pegging it in place. But it wasn't as simple as all that: the old keelson was unfair and had quite a few unsightly humps and valleys, so I spent a lot of time fairing the new keelson with fairing blocks (between 1/8th and 1/4 inch deep) placed between the new keelson and ribs. The old keelson also was crooked near the stern, which explained the tendency for the boat to pull to the left.
On the deck I moved the forward deck stringers closer together medially. This way my knees would hit the underside of the deck skin lateral to the deck stringers. Previously my knees would hit the stringers themselves which was a little uncomfortable. During rolling my knees sometimes would slide off the stringers, but now the stringers would help keep my knees from sliding.
In the cockpit I lashed in a couple floorboards. The idea here is to keep my butt from making a big lump in the skin which might slow the boat down. I'll be sitting on a doubled-over foam pad. If the floorboard turns out to be too uncomfortable I can always cut it out.
Another modification I did was to bring the forward ends of the chine stringers up about an inch to give the bow a finer entry. It will be interesting to see if this affects the performance in any perceptible way.
Lastly I brushed the frame with a couple generous coats of tung oil. I was happy with the choice of tung oil because it's thin and penetrates like water but hardens to a dry finish -- much better than the linseed oil I've used on previous kayaks, which is known to promote mildew growth anyway.