I have always like the 2nd generation 4Runner. As far as reliability the 4 cylinder has a good reputation. I have heard to expect getting a new clutch at 120,000 miles or so. If it is from a friend, it may be pretty good. You may want to look at this link, it is from a person who owns a 91, best second generation web site I have seen. In his site he talks about the lack of power, especially in the 4.
Now about head gaskets, their were actually 2 different set of problems. One was with the 3.0 V6 in the second generation and the second completely different problem was with the 96 3.4 V6. A re-call was done on the 96, so hopefully all have been replaced that needed replacing.