I have a Lobaugh Berkshire nicely finished in the C&NW scheme, but I don't have photos (yet). I have another that was specifically purchased to convert to Missouri Pacific. As Bob's posts have indicated, there were two different Mopac variants. There were five purchased by IGN, the MP in Texas. The rest were MP native. Though basically the same design as each other and the same as the CNW Berks, there are some differences. I put together this comparison shot showing the three types. Bob's MP on top, my "stock" version in the middle, and Bob's IGN at the bottom:

I used mine to represent the CNW variant instead of Bob's (nicely finished) version to make clear to myself what I was up against if I wanted to convert mine to either MP or IGN.
To me, the IGN version looks closer to the original than the MP version, which seems to have more differences, especially along the top of the boiler.
As a minimum, to convert to IGN, my model would need changes in these areas:
-- cab
-- whistle and poppet valves
-- stacks (why are there two?)
-- piping all along boiler
-- air tank
-- power reverse
Other things to note:
-- my model has an inboard-bearing pilot truck when it should have the outside-bearing style.
-- The IGN models were delivered for coal, so I could keep the original tender and the ash-pan. They were converted to oil before too long, so making those changes would be more representative of the loco over its lifetime. Not sure what the top of oil tender looked like (need to research).
-- The IGN also added the top-of-boiler, behind stack number boards like the MP version has. Again, probably best to add.
-- The IGN version had a trailing truck booster. Best to find one if I can.
I am sure that further research would reveal more differences, but I think this frames the project pretty well. Not too tough, but more changes to a steam locomotive model than I have made to date. You will know I am serious when I get the boiler dipped. Probably not this year, as I need to finish the current projects before starting another.
Jim