Early 60's specific PONTIAC GTO/ LeMans & Full size car.
(NOT known to be used in Firebird)
Pipe outlet is 3/8" which is about 9.5mm in newbie speak.....:-)
Pipes out both ends.
Fits
Fits:
1060-66 Catalina, Bonne, GP
1964 -66 GTO
1962- 66 LeMans, Tempest
1960-61 Ventura