Oddball car - swap to disc - ideas?

The Scarebird adapter plate bolts to your existing drum spindle, so doesn't matter what upper ball joint you have. If your car uses the same lower ball joint as earlier drum cars, the spindle "should" have the same bolt pattern.

You can save a lot if you buy just the adapter plates from Scarebird (~$110) and source the Toyota and GM parts locally or ebay/amazon.