Bell’s BlackGold layup was their best, at least for flat water boats.
As far as where to place a center yoke, that’s easy. Position it at the longitudinal center of gravity. This is pretty easily determined by simply balancing the finished canoe on a narrow sawhorse at its center. Some people prefer placing a center carry yoke very slightly in front of the longitudinal center of gravity so that the canoe tends to “nose up” a bit when balanced on the shoulders and then hold it down with a short line attached to the bow grab loop.
Personally I would position the seats and thwarts as best suits your needs which depends on who will be paddling the canoe. I have found that the stock placement of many tandem canoe seats to be suboptimal resulting in an excessively bow light trim.
Front seat placement depends on the leg length of the bow paddler. You need to position the bow seat far enough back to allow comfortable leg room for the intended bow paddler behind the bow flotation tank. Position it as far forward as possible with that in mind. Stern seat placement will depend on the bow seat placement and relative weight of the bow and stern paddlers. I usually figure the center of gravity of a seated paddler will be approximately 1 - 1 1/2" forward of the forward edge of the seat frame. So for paddlers of roughly equal weight position the stern seat the appropriate distance from the longitudinal center line of the boat for a neutral trim, or a slightly bow light trim as many seem to prefer.
The Northstar was usually trimmed with two thwarts in addition to the seats and the center yoke, or with a kneeling thwart replacing the stern thwart. If you are going to use two plain thwarts position the front thwart as close to the rear of the bow seat frame as you can while still assuring that the bow paddler’s back will not contact it even when leaning back slightly. The stern thwart needs to be positioned far enough forward that it will not be in the way of the stern paddler’s legs, otherwise place it as far aft as possible, between the center yoke and the stern seat frame…