Looking at experiences based on super changing 2valve 4.6 mustangs I see that people have had problems with engine failures with stangs too.
Although many factors are at play, it seems to me that 'Bad maps' and poor tuning is a common issue . So the fact that its a Ford engine in a rover isn't the reason for failure, as mustangs fail too.
Seems the engine just needs a good tuner who knows what they are doing with the 4.6 2v , not so much a 'ZT260 specialist' .
A forged build would probably be a good idea too as with any engine looking to make significant gains with forced induction.