I was thinking the same thing, find a suitable chassis and go from there. The problem the Bachmann Mogul has is that the boiler is too small, and overall seems to be a smaller locomotive. What would seem to e more suitable would be to take a Bachmann ten-wheeler and butcher it down to the frame, modify front truck to only have one axle instead of two, and then rebuild it from scaled down plans.
But, if connies were more prototypical, I know of several examples on display in the region that I can take pictures of at some point later this year. The only problem is finding a suitable frame since I don't have the equipment to make my own.
Except, I just ran across this for $200 online:
It's 1/24, but I think it could be modified pretty easily. We're only talking about enlarging it by a factor of 1:1.18. The driver wheels might be an inch or two off, but since when have I counted rivets.
Sorry Ty, but I realized that (at least for the foreseeable future) I don't have the space, so I've been pondering my next step for quite some time and I still don't quite know what it is yet. However, I can tell you that somehow, in the future, Fn3 will be a project.