Thank you all for your comments. I think I will keep the "weird stuff" at
the end of the first system; I tried it other ways and it didn't seem any
better. This is actually a v/V chord with "wrong" voice leading, although
I was thinking more melodically and less chordally.
The VI chords in the 2nd system are part of the bass line leading downward;
if the bass singers are accustomed to raising the 6th, they should be reminded
to NOT do this here (also in the 3rd measure where it's part of the
parallel-5ths phrase, again leading downward).
The story of the isosceles triangles isn't as interesting as one might
think. I use the "Encore" computer program, which doesn't "do" shape-notes. It
does, however, have noteheads used for percussion music, including a square, a
little diamond, and one-and-only-one triangle. I think it's a little confusing
this way, but better than nothing.
best wishes,
Bruce Randall