Check all coolant hoses, there are many! Not just phh, but all the various heater hoses including rear hater. If they look suspect or of an unknown age, go ahead and replace them. Look at the heater control valve (black plastic thingy at the firewall behind the engine) is it starting to look...
I just picked up a new-to-me 80 with the OME stock height replacement springs (861/862) and they handle really nice. In fact, I've never driven an 80 that feels this competent on the road. Ride is a little firm for my tastes in an unloaded truck, but still pretty good. I would do either OME...