Pretty much anything that has the same DIN-and-a-half size player. I think mine is out of a mid-90's Park Ave. You can pull the knobs off your original stereo and put them on the new one and noone is the wiser.
No, just passenger cars. If you go to a Delco warranty repair place they will have about 10 million GM units on shelves. Just spot yours and pick out a modern one the same size. At used car lots (for ideas only!) or wreckers check out mid-90's Buicks and Caddies and maybe Olds (nicer cars usually have nicer stereos); Pontiacs usually have steering wheels controls and red lighting - - not compatible unless you want to swap columns too.