A Ford drawings on 1967 Mustang dual exhaust systems. This dual exhaust system is similar to 1965-66 GT dual exhaust system implemented on 3/22/65, which includes 289 HP Mustangs. Many of the brackets and clamps are the same. This drawings is from "The 289 High Performance Mustang" by Tony Gregory, pg 77.
See "1st Generation 1964 1/2-73 - Questions and General Discussion", the "1964 1/2-65 Mustang" Section for 1964 1/2-65 installation, and the "1966 Mustang" Section for 1966 installation.
Jim