One thing you may want to take a look at is the advance mechanism on the dist. Most of them are sticking and worn after 20 years.

Most of the wear occurs with the advance weights in the cruise position. That's where the engine spends most of its time. If it is worn you can a lot of timing variation.

Not sure its your problem or not but it sure won't help.

Kevin

87 Turbo Intercooled Raider, roller cam, torsen rear diff, LSD front diff, lockup auto with modified converter, V6 brakes, low transfer case gears...