I have a 1989 Mustang LX.  The car was bought brand new by a 25 year old woman in Georgia.  It was brought to Indianapolis 2 years ago before  Ibought it.  The car was never hot rodded and never had any major service.  Although it does have 143,000 miles on it, it still runs and drives nearly perfect.  The only engine problem is that it burns 1 quart of oil every two months.  The car is all stock excpet plug wires, K&N, and a tach.  My question is would it be recommended to replace the head gaskets with this many miles on the stock engine?  I plan on doing it myself as I am pretty good with Ford motors.  What kind of gaskets are good for use on stock to mild street performer motors?  Also, what kind of bolt-ons would help pick up a few horses other than exhaust or nitrous(which I have no plan to use). 

Its normal to consume a little oil when the engine has seen as many miles as yours.  I wouldn't replace the head gaskets unless 1/they are defective.  An good Felpro gasket is sufficient.  

Should I use a compression tester to see if theres anything going on inside the engine?  I've heard people say graphite gaskets are good.

 Stock gaskets will hold up fine for stock to mild application.  Now, about that oil problem, when you crank up you car, does it smoke?  If so, does it do it all the time?   If the car smokes when starting some of the time, it is probably the seals on the valves.  If it smokes all the time while driving it, is more than likely worn cylinder walls.  Running a compression check will be a good idea.  Sorry I couldn't be of more help.    

As far as I know its just when I get on it hard, but then again I live in Indiana so it smokes when it starts up because its cold.  But the smoke doesn't have an oil smell and when i clean the tips with a rag or my finger i don't smell any oil.