Complete HEI rebuild kits include a new coil and dust cover, cap, rotor, control module, vacuum advance canister, bushings, wire harness and capacitor, spring-and-weight set and new mounting hardware. Distributor caps are also available in different colors.
Rebuild Or Replace?
Most people generally don't attempt to fix what ain't broke. However, a dead distributor or tune-up time offer opportunities to tweak the spark without breaking much of a sweat.
The decisive factor is often the existing HEI's shaft assembly. If any of its components are worn, you're better off replacing the distributor or sourcing a rebuildable core. Aftermarket distributors often have upgraded components, all of which can be purchased separately and transplanted onto an OE assembly for 'wheelers who feel they don't need a fancy billet housing. Most notable are 50,000-volt coils (for better burn than the OE 35,000-volt models), low-saturation ignition modules for increased spark intensity, high-dielectric caps with brass terminals for better conductivity, no-arc rotors, and hardened distributor gears.
Before rebuilding, make sure the shaft assembly is sound. This weight post is notched from wear (arrow), making this core not rebuildable. Although it could work, the tension on the springs would not be accurate, nor would the centrifugal weight move smoothly or consistently.
For tunability, Proform offers both its Curve Kit and complete new billet HEIs in a choice of three factory-curved versions: heavy vehicles (high-load, low-vacuum cam), medium vehicles (short-duration, high-torque cams-best for 4x4s) and light vehicles (race cams). Highlights of both options are shown here.
On its adjustable vacuum-advance units, Proform factory-sets the canister at 15 degrees, which works well for a variety of applications. Each full counterclockwise turn subtracts 2 degrees.
Obviously, the best way to find and document hidden power is on the dyno. However, wheelers who like to diddle with their HEIs can likely feel some extra poop by fine-tuning the centrifugal and vacuum spark advances.
Ready To Rebuild
Distributor guts are available as kits or individually from Proform and other aftermarket sources. If rebuilding, first verify that the core is good. Usually, shaft problems doom a distributor, but the other components can be easily replaced and upgraded. Bench-building is more convenient, but the job could theoretically be done in the field, even with the HEI still installed on the truck.
Begin by removing the cap and rotor so that the springs and weights can be removed with needle-nose pliers and screwdrivers. Release the wiring harness from the notch in the housing, and unscrew the capacitor and module to remove the assembly. | 
Test the vacuum advance with suction. If it fails or an adjustable unit is preferred, remove the existing canister's two screws and shimmy the unit out from underneath the shaft assembly. Simply reverse the disassembly process to execute the rebuild. Begin with the vacuum advance if replacing the old one. | 
Plug in the new module and capacitor harness. The module mounting area is coated with the kit's dielectric silicone lube for heat dissipation. The module and capacitor are then secured using the existing fasteners. |
Spring tension controls the centrifugal spark advance. The new weights and their bushings can be installed to maximize low-end towing power. We used the silver spring set (arrows) as referenced in the instructions. | 
Proform presets the vacuum advance at 15 degrees. Each full turn of the supplied Allen wrench retards timing 2 degrees. Once installed and set up, a few road tests are needed to dial in the exact amount of vacuum advance your vehicle needs. | 
Screw on the new rotor, and then secure the cap. The rebuild ends by installing the dust cover over the coil. Simply install and fire your engine up for newfound power. |