Here is my solution. I used 10oz Sullivan cylinder tank (link on page 1).

Modifications were:

1. Lower floor 1/4" (Photo 1).
2. Expand cut-out in tank floor ply. It needs to be large enough for entire tank to sit down under it. (Photo 2 - marked with removed areas))
3. Shave a bit off the hatch hold-down strip (Photo 2). NOTE: When I was dry fitting, I did not have this piece in place. It causes all kinds of problems as it shrinks the space between it and the phenolic tube. I expected this is why even the 8oz Dubro does not pull out.
4. Shave a bit off the bottom of F-2 (shape link cylinder). I took it down to even with the triangle stock (just in the middle) (no photo)
5. Tape tank per intructions to pull out
6. Added hole to firewall. I wanted to have the fuel line as high as possible to line up to carb so I oriented the tubes vertically versus horizon or side-by side. (Photo 5)

Photo 3 and 4 show the tank being inserted. You have to turn it 90 deg so the bump on top clears and then have it sit flat inside the fuse. Then turn 90 degress back to normal and bump it up onto the tank floor. It is hard but it fits.

I added 1/4" foam on floor, side and roof.

I agree that cutting the phenolic tube would help greatly. At first I did not want to touch this. In thinking about the above comments, I agree it is not structural but definitely gets in the way.

Anyway, I have a 10oz with minor mods that can be removed through natural birth methods.