So I spent all last night freeing up enough storage to install Inventor. Finally did it. Loaded up an STL and started messing with the fit mesh tool. Didn’t take long before I figured out how to build a surface from a hole. Started getting excited, and I tried to complete the rest of the surfaces. Then I found that it will only create planes for the rest of the surfaces. They are not trimmed to the shape of the actual part. So it looks like the only way is to do a combination of recreating all the hole geometry, and then making sketches for the rest of it, which did not seem to work very well.
Maybe I was just tired. Going to try a few more times before I throw in the towel.
Here’s what I have so far…