I will have around 700 feet of two conductors of 4/0 with one conductor of
3/0 or 2/0.
....
It is great for running 200 amp. power to your shop.
....
And the code might have big problems with the reduced gauge on he
neutral, but I'm not going looking for the chapter and verse right
now. You can use that reduced gauge wire as the safety ground and
another piece of AL 4/0 for the neutral.

I'm certainly NOT the code expert. I do know its OK for 200 amp service here
in rural Minnesota. Its exactly what I've got.

Karl