Well, I will stick with you if you want, to get deep into this engine.
I will PM you my phone numbers.
First...get this quick before it is gone.
http://www.ebay.com/itm/2002-2003-J...500-/171748880581?hash=item27fd07f0c5&vxp=mtr
Then, double check your work regarding compression checking. It is VERY unusual for all four cylinders to be down the SAME AMOUNT.
I don't want you doing unnecessary work.
If the valves were burnt, the compressions would vary....you see what I mean?
If the head gasket was blown, it is not likely to affect all cylinders equally...
Double check compression with a different gauge. Make sure you have the gauge o-ring sealing properly against the spark plug hole in the head.
Throttle open, throttle closed...makes no difference. Spark plugs out, crank engine until gauge quits climbing. Post values you get.
Be aware that this engine was made by Suzuki, and if Evinrude parts are not available, get what you need from a Suzuki dealer.
Company called Brownspoint in New Jersey has everything you would ever need, but it is full price retail.
Boats dot net also.... Local Suzuki dealer....
Or of course, Evinrude Johnson dealers.
Where are you located?