If Ford had had a suitable N.A engine on the books to compete, do you really believe that getting Prodrive/Harrop to do this variant of the engine would have ever happened???
All this turbocharged onslaught is mostly about gaining economy due to tightening regulations around parts of the world. If outright power is improved then it is a bonus, but gaining economy DEFINITELY wasn't the reason the FPV motor was developed! It was only developed because the N.A 5.0 base motor wasn't remotely close enough to the HSV competition, when put in a heavy Falcon body, to get the car onto more people's radars than the old 5.4 Boss motor ever did.