I have a sb 350 in my xj. If I were going to do it over again, I'd go with an LS motor. Zero question. Runs better, more reliable, more power, runs cooler. Yeah, you can get an old, unidentified 350 for cheap, but trust me, you'll end up paying for it somehow.
there really is just absolutely no reason to go with an old 350 these days... I hear all the time from old -timers about how computers are too hard to work on... jesus, buy a book. It's not that difficult.
either way, check out novak. They pretty much have everything you need.