Ok now I really feel bad for you. But like BajaSB said you didn't report an engine boom or a knock, etc.
Is the engine seized by the transmission? Have you posted your symptoms on the ford-trucks forum for your problem?
If so, I can't find it. If so, post a link here too.
86K miles is nothing for that engine. My bought new 1993 Bronco with that engine was running strong when I sold it at 200K. My current 1995 Bronco (bought used) at 134K has an intermittent miss/stumble which I am chasing down, but is otherwise running ok.
There may be others on this forum who can recommend a good shop in San Jose, so I hope they will.
But Occam's razor problem-solving principle states that among competing hypotheses, the one with the fewest assumptions should be selected. Other, more complicated solutions may ultimately prove correct, but—in the absence of certainty—the fewer assumptions that are made, the better.
So let's cover the facts as we understand/know them:
1. The seller told you that the transmission was a quart down;
2. You put a quart of unknown type of transmission fluid in the transmission (without first checking fluid level?);
3. The engine froze without making a knock or other sound;
4. The E4OD transmission has a very poor reputation and should only
be rebuilt by John Wood Automotive: http://www.jwtt.com/
5. The original E4OD transmission was replaced twice in bought new 1993 Bronco under my Ford OEM extended warranty under 100K.
Hmmm. Might be good to really look hard at your transmission?
Now that said, when the first two E4OD's failed in my Bronco, they failed in a manner that the engine would rev, but the vehicle wouldn't move. So your deal is different. But PM timersteel below.
Dude, if you can't work on your van yourself because you don't have a place to work on it. I get that. But I still wouldn't pay for any work on the engine until you delve further.
: send a private message ("PM") to timbersteel. He is a helpful guy and he just bought a truck with a siezed engine like yours and is still to find out if it is the transmission or the engine: