From Jim C.
81-87 distributor body was redesigned to use a larger cap. The larger cap is less prone to cross arcing inside.
It's also less prone to arcing down the outside in wet conditions. Same dual diaphragm advance introduced in '79.
The 81-87 distributor is a work of art. The shaft spins on sealed ball bearings, the breaker plate advances on a proprietary large ball bearing ring, the weights pivot on Teflon inserts, the distributor is sealed against dirt & water contamination via O-Rings, The cap provides for a source of fresh, clean air when connected correctly.
These late model distributors don't fail. The FJ60 distributors will run a long time. The only problems they develop is a leaky vac advancer and the stop pin bushing ** can wear.
The 81-87 ignitor does have variable dwell (like the newest Pertronix) and has self protect to keep from frying itself if the key is left on (like the newest Pertronix).
The 81-87 ignition is uber reliable because the electronics are not all packed into the hot, vibrating dizzy. The finned aluminum heat sink seems to be of benefit also.
Sounds like if you used the mini-truck coil/ignitor combo and the FJ60 dizzy you would have the neatest appearing setup with great reliability.