Got it done and running! The space under the smu is a little tight, so I removed the big lead weight at the back of the frame (just visible in the pic above) and put the board there. Easy! The weight didn't seem like it brought much to the table; the engine runs fine without it. I could probably reinstall it if needed. I also added cab lighting on this one. Only hard part was carefully drilling the required hole through the boiler "backhead", but it works fine.
The only dissapointment is the somewhat anemic smoke flow due to the cast S fitting that these engines have between the smu and the stacks on the boiler shell. It is quite restrctive as others have pointed out. May just have to live with it though. 
Rod
