There are die cast S scale steam engines out there. They were initially made by a company called Rex. They had an 0-4-0 tank engine (B&O prototype IIRC) and a 2-6-0 with a square tender and an 0-6-0 with a slope back tender. The boiler is the same for the two 6 drivered engines. With some additions, they could be built to resemble PRR engines with Belpair boiler/firebox add ons. Bill Lane recently showed his Rex 0-6-0 on the S scale yahoo list. That is a list that would be good to get on to ask questions. Lots of opinions and ideas there.