For this level of grouping, I'd probably prefer something related to the actual domain.
def convertDF4ToMX6(data):
# The MX6 format is read as a stack rather
# than a queue, and requires data to be 1
# indexed rather than 0 indexed like DF4
# link_to_MX6 format spec 1.3.2 (v5)
# link_to_DF6 format spec 1.2.0 (v1)
Why are we reversing and adding one? What's the reason we need to do that so much that we're combining those two functions into a single call?
This would then mean the calling points might look something like