Food combining isn't really a part of the McDougall program, but there are people here who have done it for various reasons of their own and could tell you about it.
Maybe one of 'em will see this post and respond!
One of the neat things about McDougalling is that it is possible to just follow his basic dietary guidelines alone, or even to try other things while McDougalling...some McDougallers have dabbled quite a bit in raw, or macrobiotics, food combining, or other ways to customize the diet to suit them personally. These things aren't necessary for everybody, but can be done, if desired, without interfering with McDougalling principles at all.