Jules,
here's a 4 x 8 2 loop using 036 outer and 031 inner. When the new 031 switches arrive, you can make the figure 8 crossover in the center.
Also, here's a version of the 1954 5 x 9 layout adapted to 4 x 8. Running two trains on it would be interesting without wrecking.
if you can squeeze a 5 x 9 in your space, a used ping pong table top can be found for about the price of sheet of good plywood. Then your layout options open up.