Thanks for the reply.
I have owned the 642 for several years now. It had 4600+ hours on the hour meter when I bought it, but the hour meter was not working. I fixed the hour meter recently and have performed a few repairs---a hose, carb, steering linkage/foot pedal linkage bushings and fixed a couple of leaks. Generally speaking, it is pretty tight and works well.
The compression is good, but the valve guides are worn, and quite frankly, I am wondering how much clearance is on the main bearings. The u-joint between the engine and the pumps is starting to chatter, so I need to repair that, also the engine is leaking oil at the front main and timing chain cover. Generally, I want to do a complete rebuild on the engine in the next year or so for piece of mind.