My welder, who races and does work for a lot of high speed desert racing stuff (Baja 1000, King of the hammers, etc), took a look at it and recommended I go with the kit and put them inside the spring. The radius arm wouldn't be as ideal of a spot, and I couldn't fit a 4" travel bump if welding it into the frame on the inside of the bump stop mount.
I'm not going to do the cut pictured above.. what I can do instead is cut a square hole out of the body floor, put the mount in, and then screw in a plate (with a hole drilled in the middle for the tube to protrude out of) to seal it up. Shouldn't require any welding, nor cutting of the wheel well. End result is about 3" of a 2" diameter tube sticking into the cabin. Seats and carpet are already gone, so not a big deal for me
For the bottom mount, apparently the D2 spring seat on the axle is not as wide as the D1/90, and I need more surface area to mount the relocation dish, so what I did was cut the top and bottom plate off one of a Terrafirma 2" spacer that I no longer use, and welded that plate to the spring seat on the axle, retaining the original two holes, acting like a permanent 1/4" spacer
I'm also mulling over the mega sport shock bracket pictured above, which would let me raise the lower mount on the axle, and regain the travel up top. But that'll come later, if it ever does