I know that a booster/MC from a 95-99 Breeze fits on 74 Dart brackets (w/ a little rat-tail filing). That is in my avatar and past post.
Those parts won't touch the brake pedal. The booster rod will attach to the lever in the Dart brackets. The pedal rod attaches to that lever separately in a different place (yielding a lever ratio). Obviously easiest if you have Dart brackets.
Don't know the Aspen. If it used firewall stand-off brackets too, then the question is if those will bolt to the Dart pedal bracket bolts.
BTW, you can get a new set of brackets/booster/MC cheap on ebay ($140).