First off, don't fall into the trap of thinking longer ports automatically equals more lows. Lengthening the port does indeed lower the tuning frequency. But lowering the tuning frequency does 2 things to the frequency response, it introduces more sound in the lower end of the cabs frequency capability but it also can create a situation where the low frequencies start to roll off sooner. In other words you might gain 3dB at 40 Hz but you might also move the -3dB point from 60Hz up to 90Hz, resulting in a cab that sounds less full overall.
of course in the case of the fEarful cab - the port extension was actually part of the design... which renders the above as probably accurate in a generic sense but maybe not in this specific scenario...
I wouldn't mess with the porting too much.
dead on the money there!