I like your comments regarding grains.  

From what I can determine, unless you suffer some kind of allergic reaction
or demonstrate some other sensitivity, the only concern should be whether
or not you're overloading your system with the greater quantities of
glucose that grains tend to give rise to.  

Fortunately, it's a problem that can be easily remedied by limiting the
quantity you eat at any one meal -- say, a quarter cup of grains if you can
handle them, as opposed to a full cup, as per Barry Sears' recommendations.
Even better yet, combine a quarter cup of grains, like rice, with a quarter
cup of beans (more complete protein), along with a cup or more of some
vegetable or vegetable combination, plus your protein/meat allotment.

Despite what our ancestors tens of thousands of years ago were capable of
eating, I  think something like this could prove to be very workable now.

Jim