The spool mount isn't lighter, or better. In fact, the early style K member is a better piece. The spool mount was designed for faster production at the plant.
I can certainly see where you may have a point, as through time factories usually try to cut costs. But, likewise, they usually improved things as well.
I am no expert on k members, so I honestly don't know for sure. I said the spool mount version is better, simply because the mounting system is failsafe with a through bolt through the mounts, so they cannot fail completely like the biscuit mounts can.
I would appreciate you expounding on your assertion that the early k member is superior. I always want to learn, so please, can you tell me and the others here exactly why you say that?