I don't have the MTH track library but it would be about the same as this. 36"x54" gives reasonable clearance around the edges. You could maybe squeeze it down to 32" width as an absolute minimum.
If you can spare 36"x 60", consider this variation with some O72 curves for easements. The train will flow through the curves more smoothly and with a better appearance.
If you wanted to shorten these, the straight tracks are each 10" long.
27 and 31 are the overall diameters of the curves.