Carrick was just an example, during injury crisis Ferguson would often play his experienced midfielders as CB - Keane, Carrick, Fletcher, so his younger centre backs (Smalling, Jones, Brown etc.) would be moved sideways to play let's say right back.
So looking at our squad now, Ferguson would definitely put Carrick/Bastian/Fellaini as CB, so Blind could play LB. Ferguson wasn't very keen on giving young Rafael a chance, when we all knew he was already our best right back, let alone playing some unproven, no-name player like CBJ out of nowhere.
Van Gaal is not afraid of using youngsters when needed, he even gave Tyler Blackett 12 games and Paddy McNair 18 games last season when we didn't have defenders fit for a while, while Ferguson was too afraid to play Paul Pogba when we had no midfield for like 5 years and gave him just 7 games in total. The difference is huge and credit to LVG.