The spindles are "wrong" for the application, but they will bolt in with the '73-'76 upper and lower ball joints. There's some controversy over whether the cars handle better on stock spindles or the later, taller spindles as the geometry is different. However, it seems that if there is a difference, it'd only show up in autocrossing or road racing.

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"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair

Yeah, that's what I have read as well. I have the 74 A body spindles anway. I've heard the rotors and calipers swap, and I should save the brake lines (brand new).

I am using the 5th Avenue Disc Brake assy and Spindle. That spindle is designed for a lower ball joint (actually just a lower knuckle as the lower ball joint is IN the lower control arm on those) that is THREADED where the 2 bolts attach it. I use the early to mid 70's A-Body lower ball joint which is NOT threaded. I then use 2 Truck Frame Grade 5/8" bolts fastened with a self prevailing/locking nut, NOT A NYLOK NUT.
NOTE: There is a pair of A-Body late upper A-Arms, with the large Ball joint, on Moparts.com for $100
Terry

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Terry Bogusz
From Super 6 Left turns to Straight again.

Never heard the term. What does it refer to?

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Dan ol' buddy ol' pal......
The nut I described is one where the crown is peened over or semi closed, to act as a lock mechanism. They are one time use though. Remove one and throw it away.
The bolt used with these may only be used twice (at the most) before the threads are ruined by this crimp.
These are standard USDOT approved fasteners for Truck frames and attachments.
The Hacker
LOL

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Terry Bogusz
From Super 6 Left turns to Straight again.