Port size & design, valve placement, stronger bottom end all translated into better durability in the 3-4k hp (for the time) range that kept the Hemis reputation up. That coupled with the fact Mopar actually produced an iron block back then for the guys that wanted to run a "budget" (?) fuel car that was actually affordable.
The SOHC motor was a good contender but parts availibility along with its timing change caused issues even in the "low" hp ranks of P/S.
You can dig up lots of old magizines & find Chevy powered F/Cs & T/Fers but the fact is given the quality of the parts & inherent designs of those motors back then (remember there were few if any aftermarket manufacturers) neither Ford nor GM could stay with the Hemi........