Dave,
I've just put a centre console (kept the tiller steer, just wanted somewhere for the electronics, and a base for a T Top) in my 445 Dory.
I had similar prob, couldn't decide what material, where how etc. Unless you are an aluminium fabricator or know one can i suggest a custom designed/fabricated plastic console. No not the cheap thin dodgy looking plastic ones in the boating stores, find a plastic welder or fabricator in your area and have a chat. I did just that and the end result is awesome and not too dear either.
One question, do you think a side console is ideal considering the size and style of boat. I would have thought the 4.2 would have leaned a bit with a side console and prob not have travelled well cause of that, i could be wrong.
Matt