Why not Lon Chaney, Jr? An American who often played loud and blustery types-- drank like Donlevy-- played professors in the Inner Sanctum series-- why he'd have been just as good a choice! Would have added a bit more oomph to his resume than, say, THE CYCLOPS, or THE BLACK SLEEP.

"Those aren't people- they're MONSTERS, I tell ya!"

Not that they would have taken the offer, but I think Karloff or Alastair Sim would have been ideal.

Not quite as well cast, but possibly very good, would have been Torin Thatcher.