hello, i have come here (once again) seeking knowledge.

the bus has been resting, but the weather is warming.  within
two weeks i will be swapping motors in my 81(california version), due to
an as-yet unidentified intermittent-but-mostly-present tweedling/chirping
sound (on revving/acceleration, and sometimes a constant slow chirp at
idle) and the availability of a low-cost replacement motor. i wouldn't mind
diagnosing what the chirping is before i remove the engine, so i can
fix/rebuild later at leisure.  any ideas?

the replacement motor is an 82 (non-california) which was 'rebuilt'
30,000 miles ago by a mechanic with a good reputation.  the po is not
sure exactly what that rebuild entailed.  this is my first attempt at
something this major, and i'm looking for some advice on what to check
out/do before i do the swap because i want to do it right/not do it again
for awhile.  i believe the only external symptom of anything wrong is a
leaky pushrod tube seal.  

direct replies would be appreciated as sometimes the digests don't quite
get here.

thank you, matthew and mobius