I'm rebuilding a 1945 Logan 10" which has been repainted several
shades of light gray and is now Hunter green!  I do a fair bit of auto
restoration including paint so my advise is as follows. First go to an
automotive paint supplier and pick up some aircraft paint stripper or Zip
Strip, while there also get a quart of Dupont Prep-Sol surface degreaser.
At the hardware store pick up some heavy rubber gloves, course steel wool
or scotch brite pads, a 1" paint scrapper and a cheap paint brush. I assume
you have broken down all of the componant parts to basic castings since you
really can't do a first class job if you don't do this. The paint stripper
is nasty stuff so wear eye protection and avoid contact with skin  ( it
burns) also have adequate ventilation. Brush the stripper on to one or two
pieces and wait for the surface to bubble up. Scrape off what you can then
go to the steel wool. Depending on how thick the paint is you may have to
repeat this several times till the surface is almost bare. The paint
stripper is water soluable so the parts can be washed with water ( you can
add some TSP for this job). Be sure to dry everything well..compressed air
is very helpful for this. For me the next step is glass bead blasting. I
mask off machined surfaces first. Fortunately I have a 54" bead cabinet and
a 5hp compressor but if you don't have access the stripper will work but be
sure to wash everything throughly. Glass bead has a small amount of
silicon added to improve flow so a good degreaser ie. Prep-Sol should be
used next. Now you are ready for paint.

Benjamin Moore Industrial Coatings is a good choice and a perfect match for
the original Logan slate gray can be had. You must now choose either an
alkyd base or latex based paint system. If you don't mind the smell I
prefer the alkyd materials. For a primer, Ben Moore Ironclad Alkyd metal
enamel # 71 medium gray can be used (about 9.25/qt.). It gives good rust
inhibition and can be purchased in quarts. Next is to select a finish 
material, either 2 coats of a urithane enamel or a polyamide epoxy.
Ask for shade #3417. It's not on the chip card they hand out at the paint
store but they can mix it. It's close to the original color and with a little
darkening will match exactly. Keep in mind that the epoxy is sold in gallons
( about $50/gal ) and has a pot life of only 1 to 3 days ( you need at least
16-18 hours between coats). You can squeek 5 days if you refrigerate it 
between coats. If you want a bullit proof finish do one coat of epoxy then
finish with a final coat of Aliphatic acrylic urathane (that's another $50!).
For me two finish coats of the Urithane alkyd enamel will do just fine. Note
that this used to be available in quarts but now only gallons at about $25/gal.
If you call around to Ben Moore distributors you may find some that have
the appropriate base color on the shelf in quarts. 

As far as method of application is concerned, if you have the experience
and equipment to spray that's fine. Remember that epoxy spray is dangerous
and a proper mask must be used. Though I have full spray equipment,
including low pressure guns, I'm still going to use a brush since a rough
surface like cast iron isn't going to show brush marks and with a little
care I don't have to mask.

I mentioned above that water based materials are available so I should tell
you that you can  get the Ironclad gray enamel for priming in a latex base.
A latex epoxy, shade #1609 which is close, is available in gallons at about
$50/gal. Same problems with pot life once the color is mixed. Use two coats
as above with at least 16 hours between coats. Good luck!

Grainger sells Dem-Kote blue-gray #1D469 in spay cans which is a basic
spay enamel which is a perfect match to the original Navy
Gray used on WWII and early post war Logans. As a basic enamel product I don't
know about it's duability though.