Polygon model to NURBS

The file in question is here: https://www.turbosquid.com/3d-models/3d-auto-union-type-c-model/745947

It's a 3ds MAX 2011 file. I've emailed them and they said they didn't know how to convert it from polygon to NURBS.

Here's the file

That is a cool looking vehicle.
3DS models are often notoriously bad at being translated into other formats. Many times they are simply un-stiched surfaces which look wonderful in Studio Max, but are often inverted, have gaps, and of course have no thickness when brought into another program.

I'll see if I can import a 3DS file and see what it looks like.

What are you looking for in a NURBS model? A simple solid/surface "skin", or a parametric model with clean topology?

I have an example of a laser scanned part that shows an image of how the shape remains the same, but the topology can differ between a NURBS model which is essentially a skin over the mesh, and a model recreated in a program like SOLIDWORKS.
STL to NURBS - Reverse Engineer Scan Data

It is not as detailed, but a free NURBS (SOLIDWORKS) version of that vehicle is in the Library here:
Auto Union Type C

Something I can bring into a CAD program like CATIA or Solid Works and edit. I'd like to reproduce it in CATIA but I need to measure it and it needs to be manageable.

This site implies they can send a STEP or IGES file for an extra $50.
https://hum3d.com/3d-models/auto-union-typ-c-1936/
That could be a good deal, but I'd suggest getting a partial sample of the work before committing to buy the model. The difference between a STEP file, and a good STEP file can be large.

A simple surface/solid body should be enough to import into CATIA or SOLIDWORKS, and then model around.
The work could also be done from 2D images/drawings, but working around an existing model can be a lot easier.

I always forget about this option, but SOLIDWORKS will import a 3DS file via the Scan-to-3D add-on.
I've not had many positive outcomes from this tool, but it is worth a shot if you have that module.

Most likely, but we'll need to better define Polygon Model and NURBS.

By Polygon Model I assume you mean a mesh file like an STL? Is it made up of lots of polygons like triangles covering the surface?

By NURBS we'll need to know if you are looking for simply a "dumb" solid or surface, or if you are looking for a true parametric model with a feature based history which can be edited and modified.

Both outcomes are possible, but a feature based model takes longer to create. Obviously the time/effort of the task is directly related to the complexity of the model as well.

Let me know if I can help further. You can post back here if it is nothing secret. Or we can discuss it via the message system, or email if files need to be exchanged.