The only way to tell for sure is to remove the head and look. You are going to have to remove the head in either case. Remove the head and take it to a machine shop and have it inspected for cracks and to see if it is warped.
If you suspect the head and/or the block, have them "magnafuxed" by a machine shop. On the other hand, as you're pulling it apart, check the head gasket and if it's shot, there is usually only the one problem.
There are several ways to tell if there is a cracked head in a 1987 Mighty Max 4x4 with a 2.6. Some of the ways to tell are extreme decline in engine power, suspicious engine sounds, and the color of the exhaust when the vehicle is running.
Yes! if you have a cracked head chances are your oil and coolant are mixing together and coolant and or oil is leaking out causing the vehicle to overheat... if you have a cracked head fix it! do not drive the vehicle