I had a tune-up done on it about a year ago. That included plugs, plug
wires, distributor cap, and rotor. Years ago, I bought a kit that
replaces points with an electronic unit. It doesn't replace the
distributor, just the points.

I bought a Holley carb kit and rebuilt it yesterday. No help.

Probably 6 years ago, the fresh water pump's impeller basically fell
apart. The boat overheated to the point that smoke was billowing out
the exhaust. I can't remember exactly when it started running bad, but
it was sometime after that happened (maybe the next summer). I'd think
if I had hurt a head gasket or warped a head, I'd have had problems
soon after the time I overheated it, not a year later.

I have checked the timing numerous times (maybe once per year). I
can't check it now because I can't get it started.

During the time I've been having problems with it, while running in the
driveway the boat "lopes" like it has a big cam in it. I've been told
that's an indication of a vacuum leak. That, combined with how it runs
when cold, combined with how it's now blowing fuel & exhaust out the
carb make friends of mine think its a head or head gasket problem. But
there's not water in the oil. Could this still be my issue?