
Details on the construction here:
http://www.frrax.com/rrforum/index.php?showtopic=9929
To make them work on your car you'll need to drill a ~1.25" hole into the factory spring seat, then a ~5/8" hole into the floor above it to get a 1/2" rachet extension through (to add a round of wedge, hehe).
It is also a good idea to put a tack weld on the base plate to keep it from falling out of place but this might not be necessary:

$40 shipped?