[Bushwacker]

If it were me I'd start with adding 5" extension kit to motor. Like DBL511 said, it doesn't make sense to set a boat up for a 20" motor these days, unless it's a bass boat! You'd be creating something that would be hard to sell as most new salt water motors and boats are set up for 25" shaft. Those Porta bracket/jackplates are fairly expensive as I remember from Terry's post, and there's no flotation tank to offset the stern-heavy effect of moving motor rearward. An aluminum bracket might be more bang for the buck. Just make sure to get one with a flotation tank; the more setback it has, the bigger the flotation tank should be.