Not sure what you're going off about since the clutch in the P4120758 kit has NEVER fit a 68 to 70 b body big block car at any point in it's history. It has always been too long for that application, nothing has changed.

I tried it back in 1999 and it did not fit my car back then, and there is no reason to believe it will fit in 2012 either

In 1999 it was 3 and 1/4" long.
In 2012, it is still 3 and 1/4" long.

The clutch assy was originally sourced from a 6 cylinder van application, and was chosen for minimal HP loss....not based on cooling capability, and certainly not on the ability to fit any specific years or models.