Are the frame rails wide enough to where you can box them on the inside and cut the bottom off just enough for spring travel? If so, you could drill 2 or 3 holes to have adjustable height on the front of the springs. Nice work so far!
I had originally debated doing a similar idea as yours but was actually looking at moving the spring hanger to the opposite side on the inside. Would need to notch for spring travel that way as well..
