I have an old Nishiki Olympic 12 on which I would like to change the
bottom bracket. However, I'm confused on the sizing for this
particular model.

It currently has an old non-cartrige bb bracket. I took that out, but
I don't know what size cartrige-type to replace it with. The threads
are definitely English (right side threads are left-handed and an
English-threaded Chorus bb I have fit into the threads on both sides
perfectly).

However the shell is definitely 70mm (checked with callipers and
compared directly to another bike with 68 mm shell). Do they make 70mm
bb's with English threads? I'm only aware of English in 68 and some 73
and Italian in 70.

One thing I thought of was that maybe the shell had never been faced
(I got the frame used, so I don't know the history). But I looked at
the spindle of the old bb, and it's really long, even though the bike
is a double, not a triple. The overall length (excluding the threads
on the ends) is about 128 mm, and the cones are substantially farther
apart than those on an old Ultegra spindle I have that came out of a
68mm shell.

This leads me to believe that the 70mm width is correct.

So the question is-- Is there a bb I can use in this shell? If not,
should I have my LBS face the shell? Or is it possible that the shell
is 70mm for some reason and should not be shortened?

Thanks,

Jim