As it turns out, I will likely leave the bottom end of the motor alone. I’ve had a chance to examine things more fully and discussed the engine with the owner of a local machine shop.
First, I saw that the pistons are marked “60 over”, so the cylinders have been bored .060 inches oversized—as far as they can be taken. Likewise, the valve guides were simply bored out and replacement valves with oversized stems (now long since discontinued) were used. I have no doubt that the crank was turned down as far as it could go as well.
I doubt that a valve job is absolutely necessary, since the engine was not using oil, but if it is, it will require new guides and new valves—pretty pricey. Likewise, once the cylinder walls are too far worn, sleeving and new pistons will be required. I think the only option for the crank, when the time comes, would be to find a new one.
What this adds up to, sadly, is an engine nearing the end of its service life It’s not there yet, though. With reconditioned heads, a new cam and proper maintenance, I can still get a number of good years out of this motor. However, there’s certainly no reason to pull it apart further right now.