I finally found the time to tear down the engine that I pulled out of my '93 Previa and replaced with a JDM replacement.
This engine hadn't failed. It was down to 100psi on one cylinder, and had 230k on it. I figured it was "tired".
I expected that a JDM transplant would be quicker and possibly cheaper than a rebuild, but resolved to put that guess to the test once I had a chance. That is now.

I have gotten as far as getting the head off, and so far I'm liking what I've found. I'll add pictures to this thread as I go.
Thus far I've put very little money into tools. I had to get four 12 x 1.25 x 70mm bolts to put the engine on my cheapie engine stand:




So far, following the FSM has only failed me in one place. This was just how to get the bolt holding the intake cam sprocket off. The picture in the FSM makes it look much easier than it was. I had to rig some advantage to get enough grunt on this thing. A 10" crescent wrench supported with a 2x4 held the cam fixed while I leaned on a big cheater turning a 19mm socket.



A 1/2 drive 14mm 12-point socket is used to get the head bolts loose. This will work for the main caps too. The rod bolts use a 12mm 12-point socket. Anyhow, once the head was off I could see carbon flakes pinched in the valves. Looking in the intake ports I spotted a big chunk on it's way in:


I managed to pull it out with a pair of tweezers:



All in all, the parts I've been able to inspect look to be in serviceable shape (cams, cylinder walls, piston skirts). The compression issue was probably due to carbon deposits passing through the valves. I'll know more when I get further in. I might be able to rejuvenate this engine for less than I spent on the JDM replacement and have an engine to rescue a nice discarded Previa with.
Stay tuned.