[lolife99]

I re-read your original post.
I see a few things in it that I originally didn't.
1) 4/6 drop
2) total suspension rebuild.

Like I have posted before, when it comes to "crossmember swaps",...
I say sell your 72 crossmember to fund your parts.
If you have the steering linkage, save that and use all the parts.
But from the a-arms out,... what will you re-use?
(maybe the dust shield behind the rotors)

You are buying new drop spindles, ball joints, tie rods etc.
Do you need the old rotors and caliper?
They are cheap to buy new.

Bearings will be new.
Brake hoses need to be new.
No need to swap the crossmember itself.
Since you can now buy year specific drop spindles,... in your case,... 67-70 spindles,... there is no needs to change the a-arms.

The only advantage to using the 72 parts, is that it would allow you to rebuild everything BEFORE you actually swap parts.
But I wouldn't swap the crossmember itself.