matchy:
Well I was finally able to get this easily going with a 5v pro mini and Adafruit library, so there's no need to level convert.
Did the adapter board have level converters built in? If not then you are likely to fry the
ILI9341, its definitely only spec'd for 3.3V maximum (most modern LCD controllers are
a smaller process and 3.3V I/O these days). It may work for a while, but could fail
without warning.