Far be it from me to argue religion with the Reverend, but at the risk of being labled a heretic, I understand that the extra "clean beasts" were brought along for food.
But, according to Leviticus, Chapter 11, Verse 3, Moses stated that the conditions for what was determined a "Clean Beast" were as follows -
"Whatsoever parteth the hoof, and is clovenfooted, and cheweth the cud, among the beasts, that shall ye eat."
Under this definition, horses do not qualify, and the ark would be limited to two.
Just like all LSR rules, there seems to be some points of "tribal knowledge" that didn't actually make it into the rule book. In this case, seeing as Moses was the arbiter who delineated precisesly what was "clean" and "unclean", Noah could not have known precisesly what the rules were, because Moses was a few "begats' further down the lineage than Noah. Unless horses were "grandfathered in", the ark clearly was a two-horsepower conveyance.
So if Noah was running 3x7 horses, (21 HP!) and if I were running in his class (I'm not, and few are), I might be tempted to file a challenge to the record.
And speaking of horses, Grummy, how's the motor coming?