I have been reading your thread, and i must say i'm impressed with your commitment !
One thing keeps appearing, the metric fine fasterners. Why do you need them, why don't you re-use the original one's? I used all the old ones again when i rebuild my 929 Hardtop( no RX4 ). Claened them up, a few minutes in acid and zinc-coated them myself. Problem with supplyers is, that you need to buy a complete box of one size most of the time. There is a store close to where i live, in Belgium, you can buy them one by one. Other solution is to find these bolts is at the scrappers. All older Mazda's and most of Japan-build cars use the metric fine threads.

Rear suspention parts i zinc-coated myself using a vinegar/salt bath and a battery charger.