Good suggestions from longliner!
You should always start with the simple stuff and work backwards to the complicated stuff.
You get a spark plug/s known to be working!
Pull out the one with no spark,
Fit known working one to plug lead, and earth body of plug to engine block...and have someone crank it a bit.
Watch and see that you have spark (making sure of course that the working sparkplug is gapped correct for your engine!).
When gapping a plug you will see a range of gaps (small to large) specified in your workshop manual. You always gap the plug to the SMALLEST setting because the gap will get wider as the electrode wears away!.
As an aside - you usually gap the points (if you have them) under the flywheel to the BIGGEST gap range because they will close up as the cam follower wears down!
Simple things but they help make a tune up last a bit longer...
By getting that bit wrong (i.e plug gap too wide and points gap too close) - you can tune an engine and it will run - but is already at the 'exent of allowance' for these settings because you picked the wrong end of the range for each and it can be 'out of tune' again in only a few hours as the plug gap widens beyond tolerance and points gap closes beyond tolerance!
By getting em right, the tune up will last longer as the plugs wear from smallest setting to max and points from Max down to minimum!.
Now if you have spark visible at the plug...then tis time to replace the old ones with the correctly gapped new ones and maybe you are good to go?.
If not - then under the flywheel you likerly need to go - which in truth is probably a boat mechanics job.. (But thats not the next thing to do - the starting circuit from the key is see below!)
Sometimes- the magnets stuck (glued) to the inside (underneath) the flywheel rim can come unglued with age and fly off - which means a repair job and that the stator won't work till you do!
Sometmes the wire in the stator just plumb corrodes thru and you need a new (rewound?) stator!.
Basically - you are getting into OB mechanic territory now so best try the simple things first!
Before you go from good plug to stator tho - be SURE you don't have a earthing problem in your dead mans lanyard switch circuit!
I've seen it happen, that you have the key on or switch on the Outboard set to 'run' (start) - but the deadmans switch is either off - or corroded so bad it's earthed!.
It wont start (i.e the plug won't fire) if that dead mans circuit is earthed anywhere between OB and key / switch on dash or whatever mode you have of deadmans control switch!.
Plug, battery then Deadmans circuit - then more serious stuff like points and / or stator etc - least that would be my method - someone else may know better than me!
Lectrickery never was my strong suit...
You know - turning the lights off on a moonless night (or inside a pitch black shed) and cranking while looking for a blue spark (earth leakage) is sometimes a good way to find a electrical fault....when more conventional methods might fail / be more confusing - so is listening for the earthing spark!
Probably where you should look - is at a outboard dealership - I mean c'mon a 1969 OB? You don't think maybe tis past it's use by date in 2006? (37 years old?)
I hope tis in a lake where you can swim home?