I plan on adding one of these to a newer Bachmann GP-40. The install should be easy because the drive line, flywheel, and motor sit lower in the chassis compared to an Atlas. I just have to remove the OEM board, solder a couple of wires, and I'm good to go.
for this one I didn't sorry but I did mount the decoder on the top in the rear and the speaker on the back of the frame wit the wires facing up. It is a tight fit but it works of course a SD70Ace is a little longer then a GP40. for that I would proably look at the ls4 board they make