Two short questions

[Jérôme Plût]

1. I am typesetting some music which is in 2/1, and mark using a cut
time signature. How is it possible with Lilypond to put a ℂ symbol for
a 2/1 time ? (see attachment, line 1)

2. In virtually all orchestra scores I play the alphabetic marks skip
the letter J. However format-mark-box-letters skips the letter I. So
at each rehearsal this confuses all my colleagues. Since they are
obviously slow to learn that I == J, does there exist a simple way to
make a format-mark-box-letters that uses I instead of J, or should I
start scheming something out of of make-markalphabet-markup?
(see attachment, line 2)

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