I have been absent from NAT tracks since 2004, so I cannot open my mouth about that airspace... I fly the South Atlantic routes South America to Europe with permanently published tracks between North East Brazil (Recife/Natal/Fortaleza) to the Sal/Cape Verde and Dakar FIRs, where permanent tracks are published. Very few random tracks are in use...
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As far as flying Africa, from the Southern Border of Algiers FIR, until reaching the Johannesburg FIR, I had some crossings of entire FIRs with NO ATC conracts whatsoever. ACC controllers in Chad, Central African Republic, or Zaire-Congo were... alseep, or unplugged their VHF or HF radios from the only outlet to warm-up the water for tea or coffee... or watch TV... In these areas, I often had the urge of being 200 feet above or below assigned level...
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For ARINC - the big problem with our prehistoric 747-200s, is that they have no FMS... After initial positioning of the LTN-92 INS units, we XFILL waypoints to waypoints manually to the other 2 units. Works great, accurate and no problem for lateral NAV, update by GPS... In the past, before the GPS update, it was DME update... But VNAV functions are inexistant... So the autopilot will track with accuracy, but climbs or descents require human brains for planning. The 747-400s are an entirely different breed... You are lucky...
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Happy contrails