Why the FMJ knuckle vs the 73-76 A-body knuckle?

It seemed like everything was geared toward those before. For the 11.75 upgrade they even warned against using the FMJ knucles, "Do not succumb to the temptation to use “lookalike” knuckles from later Mopars, such as 1973-up B/R-bodies, F/J/M bodies, etc. These parts, while visually very similar, are taller, altering suspension geometry (camber change, bump steer, etc.), and possibly forcing the ball joints beyond their designed range, a/k/a “over angling”."

Just wondering if that was incorrect information or what the deal is as a layperson. Plus I already have a pair of the A body knuckles. This would be for a '68 Charger.