Howdy Back Random Hero and All:
It is, at best, a shot in the dark to try to give you advice without more complete information on what you are working with. Some of the general advices may or may not be of use to you. For example, if you have a Load-O-Matic distributor, changing advance return springs will not help performance and may actually hurt the balance between carb, vacuum load and ignition advance. If you have a '68 or later ignition system, the vacuum return springs are located under the advance/stator plate, making this a more difficult job.
So, please, how about some information about what you are working with. Info such as year? trans type? any modifications? State of tune and condition of engine? How mechanically inclined are you? Help available? Tools available?
$100 is somewhat limiting, but it is surprizing what a good performance tune up and carb rebuild can do. Once you've achieved that consider-
*Converting to an electronic ignition of some kind. Cheapest may be a junkyard Duraspark II system from a '75 and later donor FoMoCo vehicle. Be sure to get all the parts of the system; distributor, module, coil, plug wires and harness. Easiest may be a PetroniX Ignitor. This is especially true if you have a Load-O-Matic distributor and the corresponding Spark Control Valve in the carb.
*Under all circumstances open the spark plug gap from stock OEM specs of .035" to .040", and increase the initial advance by an additional 5 degrees over stock specs.
Hope to hear from you will more info on your ride.
Adios, David