BCM and Head Gasket questions

[SameSevillesn18]

I have a 1992 STS with the 4.9 motor. My gauges began going out intermittently and in Ga with the temperature gauge not working I ran the car hot being negligent. I fixed the water pump issue and now I need to replace the head gaskets. These are my questions. 1)Is the BCM what's causing my gauge problem? I replaced the instrument panel and checked my grounds already. 2)I've heard of people changing the gaskets on hi mileage cars like my own and the bottom end going out. Do I need to change the oil pump too or would it be best to drop another motor in. I do all the work myself I went to my father and he wasn't sure the roots of these problems. I appreciate the help.