First of all, thanks to everyone who gave advice on finding elusive engine
problems.

Secondly, the diagnosis on my powerless, non-starting bus is that I think I
need a new head.  A compression test showed NO compression in cyls 3 and 4. 
Ugh.

Okay, questions.  Could it be just a gasket? (there seems to be a small oil
leak by #4)  If I need to replace a head, must/should I do both or is it okay
to just put one new one on?  A mechanic quoted me about $750-800 to do the job
(replace the left head) is this out of line?  I can't afford this so I'm
thinking of ordering one from GEX for $157 and doing it myself.

If I replace the head myself, are there any tricks/warnings that anyone knows
that I may find helpful?  Do I really have to remove the whole engine for this? 
Since I have an automatic transmission, is there anything special to keep in
mind or watch out for?

Last but not least, could it be a totally different problem?

Thank you so much for your help.
-Erik