I do know OMI imported at least one HO example (Diamond Series I think) with turbine engine piping inside the "B" unit. Not sure how complete or correct it is, but I'll bet it's right.......Tom was a huge UP fan. Maybe OMI would share their drawings if they still have them and this would be my 1st contact.
I JUST SENT BRIAN MARSH AN EMAIL ASKING THIS QUESTION.
I will also send an email to Dick Harley (UP Guru), as he was once a strong member of the UP Historical Society and had ties to the museum. He's forgotten more than most will ever know.