It's actually OHV (over head valves) with pushrods, if my memory serves me correctly. OHC heads take considerably more space than OHV heads, and DOHC heads even more. You'd have to raise the hood line considerably to make them fit.
even if it was sohc it makes sence not to have it dual
because the engine is allready big and emagine the size of it with dohc
just look at the ford 4.6l dohc, i could fit a 426 hemi in the amount of space that takes