Tom
Here are some photos, there is quite a bit of hacking the inner bogie to fit a decent motor, this an ABC diesel bogie gearbox and 6 watt maxxon motor. Don't be worried about it weakening the bogie inner as one reason these perform so well is that its fairly flexible once there is some weight in the loco, giving very good track holding much bettre than you would expect from a rigid bogie.
On the bogie side frames you do need to file back the bits hanging down either side of the central axle box as these catch on the centre wheel and stop you pushing home the side frame into the bogie inner. On the top side frame you can just about make out where I have filed them back, on the centre one this is waiting to be filed back and the bottom one is the side you from one that hasn't been filed back, be careful when doing it as its all too easy to take too much off.
The other thing to remember is that if you are using slaters wheels you need to remove the boss from the wheel so that the wheel is flush across its face. The wheels you see here are those Rob Thomson is selling, he may still have if you are interested, but you will need to get someone to put them onto axles for you if you don't have a lathe.
Richard