Andy,

The two boats handle quite a bit differently. The Guillemot is more 'playful', while the Spring Run tracks more strongly. The best thing you could do would be to paddle them both, and see what you like better. They are both great boats, you cant go wrong either way.

The external strongback is very easy to build and to align. While the Spring Run could be adapted to an internal, I dont see any reason to do so. Generally, changing the building methods specified by the designer make it more difficult for that designer to help with problems, because he may have a harder time visualizing the diffrences.