Thats the spindle i have but the Mopar Action article must have a few typos, it says:
On all Mopars, the swap from drums to discs (or 2-piece rotors to unicast rotors) requires one "key" part: A new steering knuckle (a/k/a "spindle.") The knuckle you need for our primary swap is from any '73-'74 E-body, or, believe it or not, any '73- '76 disc-equipped A-body (Valiant/Dart/Duster). This is a non- wearing part and perfect examples can be had at most junkyards (see fig **), but if you run into trouble, excellent repros are now available from Master Power Brakes, Inc. Do not succumb to the temptation to use "lookalike" knuckles from later Mopars, such as 73-up B/R-bodies, F/J/M bodies, etc. These parts, while visually very similar, are taller, altering suspension geometry (camber change, bump steer, etc.), and possibly forcing the ball joints beyond their designed range, a/k/a “over angling”. Also do not swap the knuckles side-to-side to mount the caliper toward the rear, this causes brake hose routing difficulties. While the correct mounting avoids these problems, on some cars you may encounter swaybar-to-caliper interference. We suggest dealing with that via other methods, described later. Using the correct knuckle avoids any of these potential pitfalls, and results in a "factory engineered" installation. Hey, Chrysler paid those engineers big bucks to get it right, so you might as well take advantage of their knowhow. Plus, we're getting it for free!
This will help you identify the needed ‘74-‘74 E-body / ‘73- ‘76 A-body steering knuckle. Casting numbers are rarely visible, so comparing dimensions is the sure way. Be sure to inspect for spun-bearing damage. Exact, drop-forged steel repros are available from Master Power (see sources.) Do not use the similar, but taller, knuckles from ‘73-up B and F/J/M/R-body cars!
And then they show the pic you've posted.
On looking at the willwood instructions for the later kit the cliper mounting braket requires drilling into the spindle, i didnt have to do that. Both kits use different inner bearing, hub assembly, and calliper bracket only, the rest of kits are identical. Different inner bearings would seem to indicate something different on the spindle shaft.
I also have the Challenger & Barracuda Restoration Guide. I think that has typos too with regards to the rotor sizes. This is what is confusing me, this book says 70-72 had 11.75" mine were smaller like 10.98 which the parts interchange manual says its from 73 or 74 (i'll have to try find some part numbers !!!
As i don't have access to another cuda to look at i have to rely on these books, guys like you and trial and error.
Only thing is an error in braking can be dangerous and expensive.
With everything on there is no play which is good.
If anyone has anything to add please do.