Ok, first and foremost I am not a fan of Force motors.
(yet I do like regular merc's)

As for the motor overheating... If your nephew is into
fixing his own motor, he should really look into why
the motor is overheating. I would NOT get the impression
that they are knowledgable when they tell me that
they replaced a bunch of parts and its still overheating.
There has to be a REAL reason why the hell this thing
is overheating. I would first check it out with the thermostats.
Make sure they are cleaned and free of sand/salt.
If they are old and have never been changed, that's bad.
The water pump impeller should be new (most common reason
for overheating)

Next if the water pump impellers and thermostats are good, then
I would check the compression of all the cylinders and see
if one is way out of wack. This may or maynot show something.
While running the motor out of the water and on muffs, I would
take an IR thermometer and see which one of the cyclinders or
banks are getting too hot. At least that'll tell you which side is
getting
too hot. You can pull the head and see if the passages are clogged
up
and replace the head gasket. Run that motor again and
see what happens. A cracked block would normally cause some
lower compression on one of the banks. They should be able to
say which cylinder is being effected.

Tom