For what it's worth, the Mopac short bay window caboose is not a transfer caboose. It's a late generation road caboose built in numbers (400 built in Mopac shops). It's frequently mistaken for a transfer caboose based on it's short length.
I believe the Family Lines versions are also road cabooses, in the same vein as the Mopac versions.
Versions of the Mopac caboose have been offered in the past in O scale brass (and other scales as well) by Overland. Currently Bluford Shops is making plastic HO and N scale versions of the Mopac and CSXT predecessor road versions. If nothing else, perhaps one of these could be used for reference.
I've had a long-standing obsession with the Mopac cabooses. When I looked at kitbashing/scratching one, I was going to start with an Atlas wide vision caboose. The mopac versions were originally going to be built by International Car Company, but ended up being built by Mopac themselves. The roof profiles are very similar for the wide vision roofs and the Mopac/Family Lines versions. I figured on sheet styrene for the bay, and some sort of screen or mesh for the platforms.
Brother Love also built a copy or several of the Mopac cabooses, fairly recently. A search should yield results about that project as well as the GN caboose on the vo-1000 frame.
Jim