How to replace distributor? Should I attempt this myself?

The P0340 code indicates a problem with the camshaft position sensor circuit. However, given the additional symptoms you've described, it's possible that there may be multiple issues contributing to the no-start condition. Here are a few things you may want to check:

1. Check the wiring and connector for the camshaft position sensor. Make sure the wiring is not damaged and the connector is securely attached.
2. Check the timing belt or chain. A broken or worn timing belt or chain can cause the camshaft position sensor to fail and can also result in a no-start condition.
3. Check the crankshaft position sensor. A failed crankshaft position sensor can also cause a no-start condition.
4. Check the fuel pressure. While you can hear the fuel pump activate, it's possible that it's not delivering the proper pressure to the fuel injectors.
5. Check the ignition system. Check for spark at the spark plugs and make sure the ignition system is functioning properly.
6. Check for vacuum leaks. A vacuum leak can cause a rough idle or a no-start condition.

It's also possible that the excessive oil on the spark plugs may be related to a separate issue such as a failed piston ring or valve seal.
If you've checked all of these components and are still unable to diagnose the issue, I would recommend taking your vehicle to a qualified mechanic who can perform additional diagnostics to pinpoint the cause of the no-start condition.

standing for a while could be stale fuel
efi or carby
is it a points or electronic module distributor
could be coil, or plug, leads points

need more info, year,make,model, is the engine light on have you retrieved all engine codes, when turning engine over, is it spinning very freely or just like it always did,
RE POST with all this info. to get a better diagnoses

Problem 5 Engine Cranks But won Start
http://www.linnbenton.edu/auto/perform/no_start.html

Engine cranks but won start

Time to meter voltage. Start with the 12V circuit. Are you getting voltage at the coil. Does the voltage fluctuate when the engine cranks? If yes to both check the high voltage circuit. Start with the coil then the distributor then each plug. You should be able to find where the spark is failing.

Cranking is Turning Over,same thing

Yes, if the camshaft position sensor has failed, your vehicle won't start.

First does the rotor turn when cranking engine?? possible timing chain is out or stripped gear..are you sure it has no spark??did you verify this with a high output spark tester ? did you spray starting fluid in the tbi unit ?

if no codes or check engine light try spraying with starter fluid if starts or ignites u have spark /no fuel check fuses and relay for fuel pump -check fuel filter fuel pump fix or replace parts -no spark but have fuel check distributor wires and plugs coil

Your P0340 is a different problem from your P0303, but they may be related.

Since the code P0340 indicates that there is something wrong with your cam speed sensor, your misfiring in cyl3 may be caused by this.

This points to addressing the P0340 error before the P0303 since it could be contributing to the 303 in the first place. Look at your cam speed sensor in cyl3 and maybe this would solve both problems at once.

Hope this helps.

Did you try looking through the fuse panels or relays?