Hey Brendan..
I had a 1989 chevy van-front motorhome with that chassis. 60K miles when I bought it and 66K when I sold it last fall.
Heads had been done before I got it. In the 5yrs that I had it, I replaced the water pump and the egr valve. I had issues with a rough idle and it took a while to find the problem. The egr is two-piece riveted together. The rivets rusted and caused a vacuum leak.
Oh, and when the water pump went, I replaced the serpentine belt and had problems with it staying on. Turned out that a mounting bolt on the air pump had broken off in the block and the new belt put more tension on it pulling it out of alignment. I took the pump off and found the belt that fit without the pump.
I have to add that it always ran good and was dependable. I drove it to Florida and back on a two week vacation after I bought it and only lost a hubcap.
Hope that helps, Bill