All: If you knew that there was no way that any company would release working model locomotives of the type/class that your chosen prototype railroad uses, which model locomotive would you purchase, for the sole purpose of tearing it apart, and reconstructing it to be a replica of the type/class that ran on your chosen prototype?
Um... that entirely depends on what one intends to model. You make no mention of what the prototype might be, so how is anyone able to recommend a starting point?
I'd probably look at some of the Japanese Z gauge because of the over the top German prices of Marklin for buying something just to cut up.
I have used a mtl gp35 chssis for my SW1000. I have no experience with chopping an AZL 38-2, but if the wheel base fits it would be a good choise.
For a diesel that is unlike anything currently made, I would just buy 2 of the SeaRails or LG Thek Brass Works power chassis. Then I would learn the art of photo etching brass or 3D design and have have a shell printed. Step 2 would take a lot of work, but for me it would turn out better than if I tried to build a shell out of styrene.
Might be easier to change scales. Most likely you model would have already been done Horribly Oversized, maybe in Brass.
Ballard Terminal Railroad's Li'l Beaver and Old Yeller. Both of these are EMD SW1 diesels. Also are a couple of steam engines, but I haven't yet decided which ones. Am also pondering modeling the traction cars from Fidalgo City and Anacortes Electric Railway.
I figured out a couple of months ago that the simplest way to construct the engine shell would be to design it using Blender, then print it out on a 3D printer. The SRPMX-1 also looks like it would suitable as the power truck for the traction cars used by Fidalgo City and Anacortes Electric Railway. Not sure if they will work for steam engines.