No Hassle A-body Headers..... It was done, unbelievable!

Awesome you got them for free.
Can only speak to early-a experience but huge improvement over manifolds.
First car i took to track(old 75/80 in maryland) was a 66 273 cuda.
Ran low 16’s basically stock. Added a set of spitfires when harold first started making em and with no other mods except for more experience went to consistent mid to high 14’s.
They work. Enjoy em.