RE: Engine Work Before Emission Tests
This may vary from jurisdiction to jurisdiction, but the general rule is Do
Not work on an engine before inspection.  The reason is simple.  If your rig
can't pass inspection even after work is done, you may be able to get a
waiver BUT only if you can show that a certain amount ( in dollars) of work
has been done AFTER you failed the test.  If the work is done before, it
doesn't count.
An exception to this would be modifications that, upon inspection, would
fail the vehicle automatically, like removing the cat or some of the other
'trick' things people do to 'improve' their vehicles.  Some jurisdictions
include a physical inspection of the engine compartment, others only look at
the actual emissions.