JDM,
I guess I followed it up in this thread : https://www.toyotavantech.com/forum/...ough#post37112
Have you tried spraying water on the distributor-just to rule out somewhere else it could be shorting? If it happens when you spray it and you have another distributor I'd swap 'em. Also how old is your dizzy cap?
From the other thread- I'm thinking after cap, wires and plugs I'd check your coil. I think Papay was right on in that thread-he spray coated his coil in rubber. Not sure how to test the coil for wet shorting besides checking resistance before and after spraying it with a mist.
Also make sure your drain holes in the distributor are clear.`