However, you can't get a precise visual without knowing the engine size (2.5L, 3.1L, or possibly a V6). The exact size, bolt pattern, and some other small details might differ slightly depending on the engine.
To get a good idea of what to expect, I strongly recommend:
* Searching online for "1990 Chevy Lumina [engine size] starter motor" on image search engines like Google Images, Bing Images, or DuckDuckGo Images. This will show you actual photos of the starter for your specific engine.
* Consulting a repair manual for your 1990 Chevy Lumina. A Haynes or Chilton manual will have diagrams and photos that will show you exactly where the starter is located and what it looks like.
Looking at pictures is much more reliable than a general description.