I've enjoyed over 200,000 nearly trouble-free miles in a similar
vanagon. I don't know what he's doing to get it to 300,000, but I'd
like to.

But what about the alternative... rebuilding what I've got? Sometimes
in the next 50K miles, I think it would be prudent to pull the engine
and install new bearings and seals, etc.

The engine burns NO oil between changes. If the pistons spec out right,
does that mean that I could score up the cylinders I have and install a
set of rings? The original crosshatching is clearly visible in my
cylinders.

If there's nothing wrong with the heads to speak of, would it make
sense to press in new guides, replacing valves as necessary, and go
with that?

Of course I would replace lifters, seals, water and oil pumps, etc. But
if the engine is in good shape, is it considered that a fairly light
overhaul will do the job, or is it new stuff from the block out?

Jim