As stated above, spark plug location has nothing to do with a motor being a hemi or not. In the above referenced SAE technical paper, page 12 under Combustion Chamber Design it states "The optimum location for equidistant flame travel is the geometric center..." Obviously, the centrally located camshaft prevents this location from being used. Interestingly, the "First Series" motors had the spark plug on the opposite side of the head, but testing of flow caused it to be relocated to the final location in the "Second Series" of SOHC engines.
Clearly, so that the motor can develop its full potential and the spark plug location design flaw that is inherent with the Single Overhead Cam design be corrected, the answer is a Cammer head that has Dual Overhead Cams!!!
At the same time, a gear drive can replace the chain, here is a one of a kind system built for a cammer motor going in a boat:
