So here's what I came up with:
2x2 box, .250 wall, about 24" long. 30* cut at the leading edge, 45* at the other.
On the topside, there's 1/2" hole accept the springs' center pin, and a 1/4" hole at the front to mount the rubber snubber.
On the bottom, I drilled and tapped a 5/16" hole, and used a set screw to position the shim, like so:
Loosely assembled, pardon the BigRock mud:
In that pic you can kinda see how I redrilled the springplate to move the axle back about 1.5", here's a better one:
Anyway, with weight on it:
And clamped down:
I should have taken a nice nice finished profile pic, but I didn't.
I was running out of time to get to work, so I threw the wheels on and test drove it around the block.