They do cover 4x5, but the ones shorter than 127mm cover it at their
intended magnifications but not at infinity - not that that's going to
matter to you, using them on 35mm.

and the snout is a lens shade. Hmm... But these lenses are

I think that the M40-M36 adapter is so that you can use the lens on an
enlarger, as this size is used by some enlargers - not 100% certain on that.
As you say, the Tominons are symmetrical lenses, so I don't see any obvious
benefit to being able to mount them reversed, or why you'd want to put them
inside the camera, behind the shutter - I imagine the shutter itself would
vignette with any lens short enough to ever want to reduce the distance from
the film-plane.  I've never seen any Polaroid literature that refers to
doing this, but maybe someone else knows.

The other tube, the one you call the snout, I do have the answer for
however.  It's for photomicrography.  The way it works is that you line up a
microscope, with a photographic 'projection type' eyepiece, under the MP-4
(or MP-3) camera head, with the shutter and this tube mounted, then extend
the camera bellows by an amount that is calculated relevant to the system
magnification of the microscope and lower the camera head so the 'snout'
encloses the microscope tube.  The shutter can then be used to take
photomicrographs onto 4x5, Polaroid, or rollfilm backs in the camera.
Polaroid refers to this item as a "Light Baffle Tube".

Incidentally, don't ignore the idea of using that leaf shutter out of hand.
You could easily enough mount it on your bellows and it would give you some
useful options.  For really high magnification you might be glad that it
introduces less vibration than an SLR's focal plane shutter; it will
synchronise with flash at any of its speeds, true it only goes up to 1/125,
but many older SLRs can't synch. at that speed; and it will allow multiple
exposures more easily than most SLRs.  There are two cable release sockets
on it: one opens the shutter up for viewing; the other cocks and fires it
(when the viewing release isn't being used, obviously.)

You might find it helpful to know the magnification ranges that some of
these lenses were designed for, if you don't have that information already:

17mm f4 Tominon 10-20x
35mm f4 Eurygon  2-10x
50mm f4.5 Tominon 2-5x
75mm f4.5 Tominon up to 4x
105mm f4.5 Tominon up to 1.5x
127mm f4.7 Ysaron up to 1x

(I don't have this information for the 135mm Tominon, would like to hear
from anyone that has.)

I have a Polaroid MP-3 that I use for some macro work with these lenses, and
have put a second shutter into a lensboard for my Arca-Swiss 6x9 so I can
use them away from the studio as well.  If I come across a third shutter
some time, maybe I'll fit one to a mount to use on my 35mm bellows as well.

I have all these sizes except 127mm to screw into the shutter, like the
lenses you have.  I also have another 75mm and two 127mms that have their
own shutters, so the shutter is between the lens groups: don't know if this
is optically any better or not, though these lenses appear to have a better
coating.  The 127mm makes a very nice macro lens on 6x9, where it allows a
decent working distance but is just a bit wider than the 150mm (an
Apo-Ronar) that I use as my 'standard' macro lens for 6x9.

Hope this is some help; despite the age of these designs, they're good,
sharp, lenses.

Peter

accessory tubes that I don't understand.

Well, whaddya know, looks like this weird little adapter is for mounting the
75mm lens inside the shutter after all - today I just happened upon this
*bay auction,

http://cgi.ebay.co.uk/POLAROID-MP-4-75mm-LENS-REDUCTION-KIT_W0QQitemZ7537704923

in which the listing quites the instructions for this thing as saying:
"The reduction kit is designed to acheive extreme reductions with the MP-4
camera, generally for the purpose of producing slides. It is used with the
75mm lens in conjunction with the Polaroid Land roll film holder.  The
purpose of the kit is to bring the lens closer to the film plane than would
otherwise be possible. This is done by mounting the lens on top of the
shutter, inside the camera, rather than below."  Sounds, from the rest of
the listing, as if there was a special lensboard to use with this on the
MP-4 that allowed you still to adjust the aperture even with the lens inside
the bellows.

Intriguing... (though, probably, not very useful today.)

Peter