I searched around and found a couple things.
Here's review in April 2006 issue, it tells how to remove the shell.
http://mrr.trains.com/news-reviews/staff-reviews/2006/02/roundhouse-trains-emd-model-40-is-an-ho-scale--workhorse
And here's a decoder install from the TCS web site.
http://tcsdcc.com/installation/ho-scale/roundhouse-emd-model-40-critter/dp2x-uk
Maybe that will get you started.
Mike.
My You Tube
I have two of the Model 40's and just purchased a Walthers ML-8 (with the LokPilot with their keep alive). As we've seen in the videos, the ML-8 will keep going over any of my unpowered frogs (mainly Atlas crossings). I would like to put the ML-8's LokPilot decoder in my Model 40's but I need to know if they'll fit. Thought I could just pop the shell off the ML-8 but its not cooperating and I don't want to break anything. Has anyone tried the LokPilot in the Model 40 and if so tell me about the fit?
john