If I EVER Start This, Boy, Will It Be FUN!!
Okay...Here's my line of thinking.
First off, I was wondering if I could leave the roof as it was, and not have to hack a large slice off above the engineer's cab. Thanks to your pictures, many examples have the curved roof continuing right to the end of the car. Phew!
Next, does the engineer have to have a separate door, or can he enter and exit through the railcar itself? Aha! No separate door required! Not only that, but if you look at the picture below, Steve Sherrill didn't cut off the end wall of the combine. He used it as the back wall of the engineer's cab. Once again, your pictures show this, too. Yay! This is just looking easier and easier!
Then, what about the cowcatcher? It looks as though I could use one from a steam engine in a pinch, although I'd like to see if I can find a nice one from someone like Bowser. I'll already be talking to them about O scale pantographs and/or trolley poles anyway...
Lastly, and I think this is going to be "The Big One", the front end windows. I sure like the big three windows on the pictures Russ (HudsonElectric) posted, although it has been shown in the other shots that I can also go with small windows too.
As we can see also, anticlimbers can obviously differ in size, as well as the placement of pans, poles, and headlights.
Bear with me as I dream here, but I'm seeing a maroon with yellow (gold?) front-end safety stripes woodside combine traction unit.
I guess my only last question is this...Would a version of this pictured combine without the radiator, and with a pantograph or trolley pole work? Would it be believable as a traction unit?