The Railroad Model Craftsman August 1982 issue has HO scale drawings of a Phase II caboose. After hunting down my HO scale rule, the portholes look to have an 18" ID and a 22" OD. That would make the porthole window frame 2" wide.
If you're looking to model one of these, keep your eyes peeled for the Sunrise Enterprises tall smoke stack. That is the correct one for this model or you can always scratch one.
HTH.
