Most old OMC's all need pretty much the same thing, assuming the rings/ bores aren't worn badly, or water intrusion into the cylinders/ crankcase, or damage to reeds, etc
If new enough (about the model year in this thread) to have the "newer" epoxy coils from then into the 70's, THEY WILL be cracked open of not having been replaced some later
At the present time, the only source I know of for "having a chance" at getting quality coils is the branded (not copies) Sierra Marine. There are some Chinese importers on eBay that are junk. They do not output anywhere near the spark energy of the originals
Regardless of what you read on the internet, you CAN NOT test condensers without a high voltage cap checker. HIGH VOLTAGE. So replace them and be prepared to replace one of them again, LOL (New does not mean functional)
May or may not need points and plug wires
Clean/ rebuilt the carb, and some can be tough, if internal passages get gummed up enough. Getting quality parts is getting tougher
Lower unit. Try to check it before you turn it over much, as if it's been sitting awhile, the water in the oil will separate and go to the bottom. You can get a "feel" for how much is there. If it's just a few drips, you might gamble on changing oil, run it part of a season, and re-check for "color." I have two motors which get by fine all season. They are not absolutely water tight, but not enough to worry about
If the motor has an oil filled gearbox, and not the older greased one, learn to rig up something to pressure test it.
Lots of parts--generally--are available on Ebay. Get yourself a service manual and parts list, although you can download most of a parts list on the 'net. usually
For me, "essential tools" are a spark gap checker such as Lisle, a standard automotive harmonic balancer puller, and a good strap wrench. SET POINTS by the timing marks and not by points gap. You can do this with the flywheel if you are patient, I use a timing tool and mag timer.
On some outboards like the 40hp, my timing tool does not fit, so I use a straightedge and "extend" the timing marks out to the outer edge of the wheel so I can see them better, "scribe"
You can also re-check them with a timing light/ external battery.
and you will have $4 
