I think Volvo homologated the disc brake/twin shock package when they did the 1964 Safari Rally. That entry didn't fare too well but the following year the Singh brothers won it using a rebuilt car left in Kenya after the '64 rally.
1965 being the last year of the 544 meant that very few cars were originally sold new with these mods although they could be ordered as extras to the normal spec. Unless you wanted to rally the car, single shocks were fine but ordering just the disc brakes was a good idea and the slotted wheels fitted for the last year helped to cool the discs. The Amazon also got the same wheels and discs as standard on all models for '65. From an engineering point of view the off set stud for the extra shock wasn't very good and by then the whole front suspension was an old design. It certainly wasn't designed for negotiating African potholes at 80+ mph!