The method I used was to make 1/8 radius cutouts on 3/8" plywood. I then offset and glued them together for strength. This would give me the 3/4" thick sub-roadbed with no connector plates. So far this is does not appear to be as sturdy as my last helix which was made out of 1x4 lumber cut on angles and biscuit jointed together. So far I liked the old method, but we'll see how it goes.
I planned on using all-thread rod to make my separation. I forgot to make the sub-roadbed wide enough, so I installed a small bracket to connect the rods. This minimizes the amount of space/height required to get over the lower loop.
I glued on the cork roadbed on both loops an tomorrow I'll mount the first turn and lay the track. Then I'll work my way up until I'm on the second level.