I have a 10:1 downhaul, double blocks on one side, triple on the other. I have a "cunningham hook" on each set of blocks, it's very quick to drop the hook into the eye at bottom of sail. And it's quick to de-rig coming into or on the beach/dock.
Seems similar of your idea of adjuster plates on either side, with pin through hole. But easier to hook in and unhook, also I think the hooks are stronger than the pins.

http://www.westmarine.com/webapp/wc...&catalogId=10001&productId=71965

or http://apsltd.com/Depts/dept1139.asp
scroll down to see hooks
I use RF8450 on my mainsheet, and I used something like SC7645 on my mainsheet downhaul blocks.

The spectra line loop with ball on other side is also very quick to rig & de-rig.