I combine SOTW with MOH for my kiddos- 6th,4th,2nd, and K (Well the K does FIAR). It works really well for us. I assign more reading or research to the older one- but that is also included in MOH.
It would definitely be easier than combining 2 cores. We do use Sonlight as a reading list, but not as complete cores. I do not know if you could cover all of history in 2 years using this approach- you would really be moving fast.