I don't know these engines very well, but the earlier engines are called 3.1L and the later are called 3100. There is another version that came later called the 3100, Series II. Although the basic engine design is the same as the old Chevy 2.8L that goes back to the early 80's, there are a few differences on the 3100 and Series II versions, mainly the front cover and intake are different. I think the 3100 also relocated the water pump and oil pump. I'm guessing the 1991 is a 3.1, while your 1997 is a 3100 (maybe even a Series II).
I'm guessing the earlier engine will bolt up to the trans., but you may have to do a lot of parts swapping, and accessories may also be a problem. Remember, I'm just guessing. Hopefully someone knows these engines better than I do.