63-66 vs 67-87 front cross member differences?????

[64-454ss]

I've read several posts/threads about guys changing the front crossmember when they add disk brakes off a donor truck. I'm curious as to why the extra work? Am I missing something? When I swapped the front A-arms/spindles from an 81, they bolted right on with no issues. Can anyone please clarify if there is an actual difference? It's not a part that wears with age. Is there a difference in track width or ride height??
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