The only issue I can forsee here is a possible reduction in bass response, or technically referred to in some forums as "baffle step". Many expert speaker/crossover designers incorporate baffle step compensation into their crossovers in order to overcome the baffle step loss in bass response which isn't as much an issue when building wider-baffle speakers such as Wayne's designs. Perhaps someone here can fill in with some more technical info about designing for baffle-step. I built my Premium Stage 4 Pi's a little bit taller and narrower than Wayne's cabinet design, and even modified the cabinet volume a bit to get a little deeper bass and I'm very happy with the performance of my system (see picture).
Regards,
Colin