I have found a 1989 Chevy pick up rear end for overdrive automatic transmission. The guy only wants $100. Can I use this on my wagon?

It would be doubtful that it would bolt right in. Any modification would not be worth the agony you'd go through. Maybe someone here has a wagon that they're parting out. I have personally sold or scrapped out 2 within the last few years, one being a good 1979 wagon positraction rear.