Good evening "Bigman", and others who may be interested,

A few little tidbits, FWIW:

The engines are most likely Chris*Craft model M or a variation of that
such as ML, etc. The C*C model M was a marinized version of the Hercules
model JXD block assembly. The JXD block dates from sometime in the
1930s, and was used in many industrial applications such as fork lifts,
"tow motors" (industrial tractors), military gensets such as the
ordnance type M-7, and on and on. In the marine application, at least,
the JXD block had a really nasty habit of developing cracks around the
exhaust seats, which can be a major downer. Internal parts for the block
assys. can probably still be found with diligent searching, but they
will be priced like pure GOLD! Been there, done that, back in the
mid-1960s (!) when I rebuilt a couple of them for a 31 ft. C*C I had at
the time. External marine accessories are problematic: they would have
to be sourced from marine graveyards, etc., or rebuild the parts you
have. The original water pump (the ONLY water pump, model Ms didn't have
a seperate circulating pump) was a gear-type pump with bronze gears. I
believe after-market rubber impeller pumps are still available for them
from Sherwood. I also believe exhaust manifolds can still be obtained
from Osco Motors (www.oscomotors.com).

You're looking at an expensive proposition any way you go at it. If the
condition of the boat warrants spending several thousand $$$ on it, I
would go with a complete replacement of the power plants with small
block V8s and Warner gears, and by all means with fresh water cooling if
your boating will be in the briny. If you are mechanically inclined,
judicious shopping for bits & pieces at marine boneyards, eBay,
Boattraderonline's engine/parts section, etc. and assembling your own
engines can save you a lot of money over buying new or rebuilt complete
units from a dealer. Been there, done that, too, and recently. I would
not spend the money attempting to rebuild the model Ms if they have been
in salt water all their life.

About the gears (or "trannies"): 1:1 would be acceptable, more or less,
because that's what C*C was fond of using in their later boats in the 30
ft.
range that were equipped with V8s. For better efficiency, 1.5:1 gears
would be better, but a bit more costly. Even better would be 2:1 gears,
but you probably don't have enough clearance to swing a large enough
wheel (prop) to properly load the engines. In any case, you're going to
have to change the wheels if you go with a small block V8 replacement
for the model Ms. You can should be able to use the same shafts IF they
are not scored by the packing gland and/or the strut bearing.

Large problem with putting V8s in an old 30 ft. C*C: Clearance over the
top of the engine. The model Ms were (are) "bass-ackwards" engines,
i.e.: the flywheel is forward. Overhead clearance is not an issue with
them. Many, if not all, of the small block V8s that C*C used were also
flywheel-forward engines, *AND* had more-or-less low-profile intake
manifolds to minimize the overall height of the engine. Unless you go
with that type of setup, and instead go with a now-conventional
flywheel-aft setup, you will PROBABLY have to build little toe-stubbing
doghouses into your engine hatches to provide vertical clearance for the
carbs. Bummer. One way to avoid that problem (which I have done) is use
Chrysler 318 (series) small block engines. Chrysler used to make a VERY
low-profile intake maniflod for that engine, and used two Carter side
draft carbs (YF?)that hunkered down in the vee of the engine so as not
to require the overhead clearance of a more conventional arrangement.
Those engines were flywheel-aft units. That's a stretch, and the
manifolds & carbs would be super-hard to find, but...

Another consideration, if you go with newer engines, is engine controls.
Particularly controls for the gears. Most C*C model Ms had rigid
mechanical controls for the gears, whereas more modern engines with
hydraulic gears like Warner or Paragon use push-pull cables. That means
you would have to have throttle and gear control units for each engine
(pricey!) and the cables themselves. But maybe you're "lucky" and have
the vacuum (or was it electromagnetic) abortion C*C called
"Chris-O-Matic" gear controls, in which case (IIRC) things would be a
little simpler. Maybe. And of course, a modern engine will have a 12
volt electrical system, which means changing all your instruments from 6
volt units to 12 volt units or cobbling up a 12-to-6 volt regulator to
run the engine instruments. Then there are the bilge pump(s), and
whatever else wants 6 volts, to contend with. Light bulbs for nav
lights, etc. are the cheapest things you'll have to contend with: change
them to 12 volt bulbs - the wiring doesn't even need to be changed!

All that being said, I would STILL go with a complete change to more
modern engines of some sort if I really wanted to USE the boat rather
than play nursemaid to those poor old C*C model Ms/Herc JXDs.

Sorry for rambling on, just though I might pass along the benefit (?)of
40+ years of experience "messing about with boats". Lots of boats!

Ed Greeley