Some points to consider:
1) The availability of new mechanical SLR's is essentially zilch, whatever camera is purchased must be economically serviceable.
2) Used lenses are a crap shoot (in that it may be necessary to purchase multiple copies to obtain a decent optic). Note that a used lens is also likely to require servicing.
Remembering the above points, lets consider the requirements (assuming, of course, that they are written in stone):
I'm looking for something reasonably compact, using modern batteries for the meter, mechanical, with a bright viewfinder that can take a diopter lens or adjusting.
Assuming that "reasonably" compact excludes cameras such as the Nikon F series, IMO, the options here are:
1) Olympus OM-1n
2) Nikon FM/FM2
These bodies can be economically serviced and the OM-1 can be modified to use the S-76 battery. Diopters can be found for both.
Would need a 35 and a 50, both with comparable quality to modern summicrons.
Both Olympus and Nikon have a selection of excellent 50mm lenses.
However, with regard to the 35mm focal length, IMO, there is no Summicron equivalent from either company. (FWIW, I have owned them all and have NOT been impressed with any.)
Fortunately, the Zeiss Distagon 35mm is available in a Nikon mount. While this lens is not exactly cheap (or small), it is by most accounts, an excellent optic.
So, in conclusion, the only body that fully meets the stated requirements is the Nikon FM/FM2.
The Olympus OM-1n is only an option if the OP can relax the 35mm Summicron equivalent.
