Headers 273 body a

On the 66 - is the car manual or automatic? If it is automatic - is it column or floor shifted? If column shifted - you have trouble

Floor shifted should work - if you haven't made the change you will need a mini starter - many options

Long tube headers are the best, there are also some block huggers, which cost a little less and can be a little easier to install. I run Sanderson DD8s

Most of all - read the complete instructions for the TTI/Dougs.