On the gunnel supports, are you building a cap from scratch or re-using the old cap? Frizz is right, hard spots at the gussets could be an issue. An alternate approach would be to use a thick core in the cap and make it look like an inverted U, overlapping the hull on the outside and extending down several inches on the inside. The vertical legs of the U create a lot of stiffness and extended all the way down to the deck on the early Moesly CC's. You could get similar stiffness with a shorter and thicker leg, maybe with a rib along the bottom of it. The best way to attach cap to hull would be glass tabbing with epoxy on inside and outside; next best would be to use pop rivets or machine screws; weakest joint would be to use tapping/sheet metal screws with sharp threads that cut the glass fibers and tend to come loose.
If the entire inner liner has been removed, I'd recommend adding balsa core to inside of hull ala billythekid's thread:
http://www.classicseacraft.com/commu...ad.php?t=24262
A tall thin beam/stringer is very stiff in vertical bending but it'll tend to buckle if it's not supported from the side by bulkheads. The original boats didn't need many bulkheads because the cockpit sole was well bonded to tops of the stringers over their entire length, providing significant transverse stiffness. This bond is important, so I'd use epoxy thickened with glass fibers to bond the deck to the top of the stringers, even if poly or vinylester is used everywhere else.
Regarding stringer attachment, I doubt any reinforcement is needed there because the 4-stringer hulls were really well made, with the glass stringers being installed about halfway through the layup. The stringer tabbing is extensive and thoroughly explained in great detail in the Boating Magazine article on the 1969 Seafari 20 in the Literature section. (To get to it click on Classic SeaCraft Home in the blue bar at bottom of page, then click on Literature tab.) I think that is a .jpg file however, so not very readable but I can send you a very clear .pdf version if you PM me with an email address.
If you're planning to install a bracket, I'd suggest you read my Pros & Cons thread at top of this section. Sounds like you're already moving the gas tank forward, but you might also consider moving the console forward some as well. Although the stock 20' hull is extremely stiff, it's relatively light with less beam than modern 20's. This makes for a great ride but it's more sensitive to weight and weight distribution than a heavier fatter hull, so it's good that you're asking questions and paying attention to this stuff before you get too deep into it! Welcome aboard and keep us posted on your restoration! Remember that good pictures are worth a lot of words, plus the guys on this site love boat porn anyway!