This exact same issue was brought up here a couple of weeks ago. Suggest you search for "dougs" or "dougs headers".
IIRC, the linkage you are referring to is the one that locks the transmission shifter and steering column when the key is removed from the ignition switch, the new for '69 theft deterent system.
The discussion said that most likely the locking linkage had to be removed - but I do not remember if the Original Poster ever came back and said that for sure.
2012 Mustang Boss 302 #1918, Competition Orange. FGF replacement 2006 Mustang V6 Pony, Vista Blue. Factory ordered. 2019 BMW X3 (Titled to the wife, but I'm always driving it for her. So I'm claiming it) Old projects, gone but not forgotten: 1967 FB 400, original CA car. After 22 years of work, trashed by the guy who was supposed to paint it. I had to sell it. 1980 Turbo Trans Am 1970 Mustang fastback, 351C 4Bbl, auto 1988 Mustang GT, 5 speed 1983 F-150 4x4, built 302 1994 Chevy K2500 HD 4x4, 454 TBI
