The "Illustrated Facts" book, under the heading of "Engine Exhaust Systems" is certainly confusing.
On page 29 is this gem:
"All Mustang GT models are equipped with a dual exhaust system. This system consists of dual exhaust pipes, and [sic] equalizer pipe, dual "node" chambers and resonators, dual exhaust outlet pipes, and dual chrome exhaust outlet tips extending under [my emphasis] the rear modesty panel. This same system, with the exception of the chrome exhaust tips, is included on all other Mustangs equipped with the 289 - cubic - inch High - Performance V - 8. All other Mustangs are equipped with a single exhaust system."
The page then has a chart that obliterates a lot of what was just said and shows only 289 Hi-Po and 390 cars got dual exhaust.
So, the first sentence is wrong (according to the chart).
The paragraph indicates that all exhaust goes under [my emphasis] the modesty panel (aka valance/valence) and then goes to say the Hi-Po does not get the dual outlet pipes. I wondered where I got that idea from.
Page 22 say the the GT Equipment group includes " . . . -- plus dual exhaust system with bright "quad" extensions [not "dual . . . tips"] on 390 and 289 High - Performance V - 8".
Then finally, and appearing nowhere else is the note on page 30 that the Hi-Po is available only "(with GT Equip. Only)"
This whole business of what is correct with respect to dual exhaust has been muddled by the "facts" book.