Thanks for the suggestions guys. Well, tonight I took the plunge and removed one side with a circular saw. I was really impressed on how clean the cut was. What I'm really unimpressed about is the thickness of the new sides. In fact they would have to be at least double the thickness of the originals! So I've now decided to just leave well enough alone and build the IM kits without the new sides.
Body mounted couplers, reduced ride height, some extra detail and FV wheels should make for a nice string of cars. I'll also have to dig up the Tom Mann weathering articles to complete them.