Before buying anything, I would pull the head on the '88, and see how bad the damage is. Look to see if the piston is cracked, how bad the head is, etc. If it's minor, and I expect it will be since only one cylinder is bad, you would be better off having that head fixed, and keeping the '88. If the damage is severe, and the piston is cracked, then go for the '91.
Take care,
~Chris