The good news is that Aspen brakes will fit; the bad news is that you won't be able to keep the small bolt pattern if you use them. To install the Aspen (F-body) brakes, you'll need a set of upper control arms from a '73-'76 A-body, '66-'72 B-body, or any E-body. Get a set of '73-'76 A-body disc brake ball joints new from any parts store, and the spindles from the Aspen will bolt right on. The parts you'll need from the donor car are everything between the ball joints.
Or, for really big brakes, get the hardware off a '75 or later B-body or R-body. That's things like the Chrysler Cordoba and Dodge St. Regis. It installs just like the Aspen hardware, and gives you nearly another inch of rotor diameter. Check out this article for the notes on different spindles:
http://www.bigblockdart.com/tech/spindles.shtml
If you must have the small bolt pattern, though, you'll need a '72 or earlier A-body disc setup. Lou has already done a great job of covering that option.
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"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair