Well, after the cooling system R&R and ignition system work, it looks like I
do indeed have a head gasket (or more likely O ring) leak, blowing air into
the cooling system.

I am getting air constantly entering the cooling system on my 5500 mile
rebuild.  I have tried bleeding the system but air returns.  I had the heads
re-torqued about 700 miles ago, and that seemed to help it for a while, but
it is back, bigger than ever.

Only one of the heads was re-torqued, the bolts on the driver side would not
move, so I am pretty sure the leak is on the passenger side.  I would like to
get as much of this figured out before I approach the shop who installed the
engine.

Can I use a compression test/leakdown test to figure out which cylinder(s) is
leaking, or is likely to be leaking?  Is this a matter of buying a cheap
pressure guage and attaching it onto the spark plug threads?  Is there any
advantage to having an experienced shop do the test?

How do I do a compression test?  hook up guage and hand-turn engine?  Is a
leakdown test just timing how long it takes for the pressure to leak out?

thanks for all your help.
Peter & Zippy