I have changed the starter on several GM "S-10" sized trucks and one on a '91 Suburban (square body), and taking about two hour to change the starter sounds about right.
You some times need to shim the new starter to get it to engage properly. I got lucky and never needed to do that, and it still took me over an hour to change the starter myself with the knowledge from doing it before.
The starters for the 4x4 IFS trucks OBS/NBS/NNBS (I'm not sure about the 2WD IFS trucks) are a lot more expensive than the one used on the old square body trucks.
At the time that I had to replace the starter on my Suburban (In the middle of winter, in a parking lot. Not recommended
), they were $35. If I needed the one for the IFS truck, it was about $150.
The flange and everything were the same, but the one for the IFS truck is a lot shorter and smaller around than the cheap one. You need the smaller starter to fit between the bell housing and the front differential. I think at the time, if you had a 2WD S-10 (at least with the 4.3L V6) they used the full size starter.