Re-working with AC Delco & Delphi HEI electrical parts and Moroso or Accel or ... mechanical bits is not any more expensive than the cheap Asian knockoff distributors.
Cheap Chinese electrical parts are usually miserable excuses for parts. Delco and a few others have the resources to ride the manufacturers like a $2 horse so they get a quality product. The Chinese manufacturers then sell the rejects to the second and third tier outfits.
If you use quality internals then you'll have a good working distributor that'll last instead of one made from floor sweepings.
The broken plastic piece is part of the module pigtail. You can buy the AC Delco D221 "radio antenna capactior" (HEI module to coil pigtail and condenser) for $19 on Amazon.
Electrical
AC Delco Professional D221 Module pigtail and condenser $15-$20
AC Delco Professional D1906 or Delphi DS10071 four terminal Ignition module $20-$35
AC Delco Professional D1907X Pickup coil for V8 $40-$45
AC Delco Professional D504A Ignition Coil $55-$70
MSD 8416 Brass contact Cap & Rotor kit $30-$40. Red MSD equivalent to the no longer made Standard Blue Streak DR450X cap and Standard Blue Streak DR318 rotor.
Accel 170072 is a nice foolproof BAT and TACH connector. I'd use one of them if your 40 year old BAT connector is hammered. You can extract the Packard 56 terminal from the stock BAT connector and the Accel plug and then insert the vehicle wire terminal in the Accel connector. If you don't have a tach just put some heatshrink over the end of the tach wire to cover the open copper end or remove the tach terminal completely from the Accel plug.
Mechanical
Moroso 26140 Distributor gear shim kit around $9
Moroso 26150 Distributor body shim kit around $9
MrGasket 929G or MSD 8428 advance kit... I usually use springs, E-Clips, and plastic bushings from these kits with the original weights... Usually costs around $10
Accel 31035 Adjustable Vaccum Advance Can... If your original advance can isn't leaking then don't replace it. Around $15-$20
Axle grease for the grease pocket at the top of the shaft.
Disassemble the distributor.
I don't agree with his assessment of aftermarket coils and modules. It might've been true in the 70's but by the 1980's GM did some work on the ignition coil and module. Delco and Delphi electrical parts will be reliable for a long long time. Most of us are not driving race engines at over 5,000 RPM... more like 2,000-4,000.
http://www.rustynutscarclub.com/HEI.htm
If the bushings or shaft are damaged, or the advance is seized, get another core.
Take a picture or write down whether the advance weight ID stamps are up or down.
Clean the hard parts that you'll be re-using.
I usually blast the body with walnut shell after a dunk and scrub in Kerosene using a bottle brush and plastic bristle scrub brush. I leave it for a couple hours in the sun to dry before it goes in the cabinet. Stuff a cork or Kleenex/TP in the shaft holes to protect the bushings and rinse again with kerosene and a bottle brush and plastic bristle scrub brush when you're done.
The advance weight assembly usually cleans up by hand with Scotchbrite, a toothbrush, and kerosene even when it's rusty.
Any varnish will clean right off the shaft with Kerosene and careful scrub with a toothbrush.
I grease the rotor mount bushing with a thin layer of heavy grease on the distributor shaft.
The cam mating gear, thrust washer, and the shims usually just get a rinse in Kerosene ad a dip in motor oil.
Make sure to replace the crusty grease in the wells under the pickup coil with some high temp heavy grease. There may be a plastic grease well cover. I don't know where to get replacements for those. I just fill the wells and put the original back if it's not falling apart.
You want the gap between the gear and the distributor body to be 0.015" to 0.020"... closer to 0.015" is better. I usually find the end play to be well out of spec. A wider gap will cause erratic ignition timing. This simple setup issue causes a lot more trouble than it's worth if it's skipped.
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I've had distributors ride tight against the oil pump... usually with aftermarket intake manifolds. Shim between the distributor and the intake to lift the distributor body til it doesn't hit the oil pump drive. Spec is something like 0.030" to 0.040". I usually go with "It doesn't hit the oil pump drive anymore."
If the heatsink paste included with the module isn't in good shape or there's not enough to coat the whole module and mounting pad I use CPU Heatsink paste. I have a tube of Dow 340 Silicone Heatsink Compound that I used on the PMD on my DS4 Injection pump. The DOW 340 paste works great on HEI ignition modules. 3 oz tubes of SuperLube 98003 Silicone Heatsink paste are around $6 works just fine. DO NOT USE DIELECTRIC GREASE it's not thermally conductive enough.