Ok I went the easy route and trimmed down the plastic housings and araldited them to the cages. the motors mount up ok, and I've given each of them a test run and they all seem to run smoothly.
The next step is to wire in the speed controllers. I have the electronise to hand for starters, as I only need to stick a couple of crimp fit connectors onto the wire to get things happening.
Then I need to make the wheel hubs.. Might get some of it done this week, but I really am in no rush at all.