hi Paul,
i tried to draw it with a 18" radius and #4 atlas c83 turnouts. These switches are actually #4,5 not as steep as the switches used in the MR plan.
Width-wise i came 4 inches short, i needed 4' 4" or 52 inches. Due to the longer Atlas switches i needed more then 9 feet for length.
Using a 16" radius and real #4 turnouts e.g. Peco might make it doable on a 8x4. Often said on this forum a 9x5 pingpong table would do great. BUT looking hard at the plan, it should have access to three sides. the needed room space will be about 12 x 10. with the 9x5 table as a starter; pretty large. (11x9 with a standard 8x4)
Paul
Measuring the plan, it is 2 x 4.75 inches. Scaling directly up to 4 ft wide, the length would be 9.5 ft. Using 18" radius and #4 turnouts you might be able to fit it in 4x8 if you lop off half the harbor.
I suggest you redraw the plan to scale on graph paper using turnout templates and a compass, or one of the popular track planning software packages such as offered free by Atlas.
Good luck