The 5.0L is the superior engine in my opinion-it ran for nearly 30 years in that displacement alone, 35 if you count the smaller 289 and 260. I'm not real big on the 4.6L, not that it can't make lots of power though. The only real add ons he has that would make any noticeable power is the throttle body and coils-maybe. The h-pipe by itself would be negligible and the shifter does nothing for power. His throttle body may be bogging down his engine a tad if that's the only fuel add on as well.