I'm no expert on this, especially with the 20', but I would expect that so long as you get a bracket with enough floatation to offset the additional moment arm from having the engine 30" vs 26", longer is the way to go. Most everything that I've read indicates that a longer bracket (given it has enough floatation) acts like an extension of the boat and generally improves the overall performance.
I'm just finishing my project (23' with 30" bracket - by Don Herman @
www.hermco.net). I pick it up this morning so I can't say for sure how it'll perform. Just my two cents. Good luck.
