Thanks to all who responded.

No, I didn't get any documents with the rebuild, other than a bill. :(

It sounds like the consensus is, for 1000 miles, an oil change for
sure, and valve lifter adjustment maybe (but perhaps only if they are
noisy?).

Second question:  I've been running with the O2 sensor disconnected
as per the installing mechanic's recommendation.   I'm a little fuzzy
on his reasoning, but I think it was a combination of the idea that
running rich was good for a rebuild.  With the O2 sensor connected it
seemed to be running lean, and it wasn't worth adjusting the mixture
since the piston rings etc. needed time to seat in anyway, so it was
better to just run rich for 1000 miles and then adjust it later.   Is
this nuts or was the mechanic just b.s.-ing me?

In any case, I'm at 1000 miles, so time to move on.   If I leave the
O2 sensor disconnected, the van runs great, but only gets about 14mpg
on the highway and is probably laying waste to the environment.
With it connected, it gets around 17-18, but has moments when it
stumbles on acceleration.  The O2 sensor is new.