Humm, ok. I presume that's a thunderbolt ignition on that one.

I do recall that Merc used to use a tigger that was located in
the distributer. How many coils are located in there?
Some had one coil per cylinder, others used one coil that
went to a distributer.

If you look at the distributer assembly, there should be 2 or 3 wires
coming
from it that goes to the power pack. That in effect is the trigger.

What you need to do is make sure that you are first getting power
to the power pack. From there you can have the ignition key on,
(leave the existing spark plug wires the way they are) and
put the positive side of the volt meter to the low voltage side of the
coil (this would be the wire coming from the power pack)

With this connected you can manually move the flywheel. You
should see the needle on the volt meter bounce quickly then
stop. If you use the starter it might go by too quickly to realize.
(its basically sending a 12volt signal to the coil. The coil should
energize and create the spark. (when you are doing this, the
key needs to be on the ON position to throw power to the power
pack!)

If you are getting power to the coil and that's it (no spark), you most
likely
have a bad coil. If there is no power going at all to the coil
from the power pack, you need to check to make sure that the
trigger is working. Pretty easy thing to check, its only a switch
that turns on and off depending on its location at the moment.
I believe that there 3 wires going to it. One is power and the other
two are the switching mechanism. You should see something happen
when you turn the flywheel.

If its not doing anything then you can have an issue with the
distributer.
The trigger on that is built into the unit, so a new or used
replacement
would be necessary.

If you really want to get move involved, try a local boating store and
get the shop manual. They have generic information like I provided
above but may be a little more in depth. You local library may have
something too, and that's not going to cost you anything.

If you are looking for parts or another motor, you might want to check
out ebay. A quick search on there turned up a few motors of that
vintage
in different parts of the country. If your lucky it might be close to
you.
Might be worth it considering the distributer on these things are
expensive
and somewhat hard to find.

Tom