Ground brick,
You've stated that HF is not an option for data transmission but on the latest HFDR(high frequency data radio) equiped aircraft data transmission by the ATSU is indeed possible.
This aircraft technically didn't have a ACARS system instead it had a ATSU which acts as a router of data from the FMGEC, CMS or FIDIMU to the VDR(VHF data radio), SATCOM or HFDR depending on selected customer options.
The hardware functions of a ACARS CMU are carried out by the AOC software in the ATSU.