The writeup at 12V.org says (4) O2 sensors for a 97. (2) before and (2) after the cat converter. I know the front ones can be access from the hood but can the rear ones be access by jacking up the car?

They're on the back of the cats. Jack/jackstands or oil change ramps will give you easy access. If you're skinny, a couple of boards would probabaly give you enough height (though not comfortable).