Khmer tally-style numbers

[Richard Wordingham]

I have come across some tally-style numbers in old Khmer
inscriptions and I'm wondering how they should be encoded.  I am
assuming that the alphabetic script is Khmer.  What characters might
be being used here?

If I use a sans-serif font, the Roman numerals I, II and III work
well.  Other possibilities I have considered are U+1D369 COUNTING ROD
TENS DIGIT ONE to U+1D36B COUNTING ROD TENS DIGIT THREE and up to three
instances of U+1D377 TALLY MARK ONE, which the chart calls a 'western
tally mark'.  Are any of these formally appropriate?  For high numbers,
e.g. '6', the texts seem to use ordinary Khmer decimal digits.  It
feels massively inappropriate to use single vertical stroke character
U+17F2 KHMER SYMBOL LEK ATTAK PII for a pair of vertical strokes
together meaning '2'.

Richard.