IF the plastic shells are accurate, there has been a large selection of detail parts to detail them out. This has been true for years. In the 80s, I took a pair of the Old Atlas/Roco F9s and made a pretty close PRR F7 out of them. I shaved off all the cast grabs and railings and removed the steam generator stuff on the top. I put on wire handrails. I moved the front portholes on the side to the correct location and replaced the pilots with passenger style pilots ala PRR. I also added trainphone antennas. At the time, they were the most accurate and detailed plastic F units available.
PSC, P&D, Des PLaines to name a few make lots of lost wax detail castings to customize most diesels. It can be done today.