I'm good at faking it To draw the radial drill I got one dimension from a chart on the manufacturer's website. That model had a 17" diameter main column. I used that as a gauge to put the rest of the machine in proportion. For the diesel locomotive engine, I went on Google, searched from EMD 567 engines and found pictures that showed the best detail. Then I used the Match Photo feature in SketchUp that lets you do a reasonably accurate 3D drawing.
This image shows my drawing over top of a 567 drawing. It's not an exact match. That may be due to the distortion incurred depending on the type of lens or focal length used to create the original image. But I'm not looking for a mathematical model. I'm looking to create a good looking, complex model that will inspire. It's going to be a diorama at a distance so rivet counters won't get too much to look at. Lastly, I've yet to find a set of drawings that could give me really accurate sizing. I started the model with a good cross-section cutaway drawing. I looked up the bore diameter and then scaled that drawing on SketchUp to exactly match that distance thus putting the rest of the drawing in scale. You draw in 1:1 scale in SketchUp. I then scale down by a factor of .021 to get to 1:48.
There's some much going on in the front end that it's quite a challenge to pull it apart to model it. Right now I'm wrestling with that plenum that's sitting below the roots blower at the engine's rear. The other challenge is I believe this engine is a marine diesel, not a locomotive. I know that because it has two water pumps (which I drew because they look cool). One is for fresh water and the other is for sea water and there is a heat exchanger for engine cooling. I'm also going to model a main generator so there will be no confusion.
The best approach is get SketchUp, start using it and start studying images that might work. If you screw up, so what, it's just 1s and 0s on some enhanced silicon chips.