Tom
with all due respect,
why would specs call absolutely for handcarved?? If the purpose of these signs is to say Welcome[sic] then cnc carved should be fine. Your main concerns appear be final product appearance [hence the gold leaf],and structural integrity.
If someone in the committee is adamant about " handcarved" then they either A;
don't know what they are talking about or B; have an agenda.
As per Komacel[pvc] vs HDU. both have their pluses and minuses.
properly installed neither should crack/split/
Be danged if I would warranty goldleaf over pvc for an exterior sign though. too much thermal induced movement.
good luck
Carl