I've found bluebook to be useless when it comes to boats and motors. Just my two cents but I'd go with the Alumacraft. You'll be glad you have the 8 extra inches of width. It's a much bigger deal than you think for stability especially if you plan to deck it. If you're selling the motor, who cares if you make an extra $100 on one or the other. That extra $100 will be worthless if you kick youself in *** for not buying the wider boat down the road.
I wouldnt think 2x, I would get the 48 boat, I cant see you getting more than 1200 bux for the motor, which means you still have 1500 in the boat and trailer.. the 42" boat isnt worth 1500 IMO..