Mark, I would recommend raising your coolant pressure cap fill spout assembly as high as you can and perhaps putting a 45 where the vent hose attaches to the Head. You want all air to vent out of the engine up to the spout to prevent airlock/ pocket overheating.
I'll try to get some pics after work tomorrow night. This is a Matco unit, you might give them a call, probably can buy complete for less money and the engineering is done. I don't know for sure if the spring section is solid or hollow, guessing solid, steel but unknown alloy.
You should be able to purchase an RV6A assembly (the one of your pics with the unfinished wheel pant). That's what I have on mine (including Avid drawings for same). I'm planning on taking mine off later this year to install Grove taildragger gear I purchased. Thought about selling it but I'm kinda thinking of hanging on to it as a boost should I sell in the future when the Bearhawk is done. Although I'm really falling in love with this bird. Thinking about the possibility of the enclosed trailer route for retirement ( or pre-retirement) travels...
As Ed mentioned, it also provides stabilizing compared to the original style Avid nose gear as it puts the wheel farther forward.
Free floating would be good, unfortunately with the original fiberglass tanks cracks can develop from the stresses even without ethanol. :o( I like the idea of rotomolded, not sure how much weight gain there would be though.
Without crunching any numbers, you have A drawn in at 45* to horizontal. Any upward wheel movement would be greater than outward movement from that point up, very close at that point. Were you thinking 4" spread between the two wheels? Only 2" upward movement before spring bottoming would be of great concern to me. Better buy bushwheels and keep the pressure low. ;o)