As I recall, the 412 has a 27.2mm seatpost. That interchanges with most 531 bikes and other better steel frames. The bottom bracket should interchange with most Japanese and English bikes, though many Raleighs won't take it. The brakes will depend on the wheels as well as the frame.
There are some good deals on Japanese Schwinns and Raleighs out there if you can't find a Trek but Treks are hard to beat. I've got a 24" in the basement that I can't wait to put back together.