You do not need to be revving the engine very high, or be "Looking to squeeze the last HP out of the engine" to notice the improvement headers make over the terrible FE log exhaust manifolds. Years ago, I got tired of replacing cracked log exhaust manifolds on the FE in my 74 F350, so I installed a new set of Hedman long tube headers , along with a basic dual exhaust system. The performance gain was very noticeable, basically from right off idle and up. I rarely revved the 390 over 3500 RPM, freeway cruise RPM was typically 2600-2800 RPM. Although the headers never leaked, I did replace them after 14 years, just because they were looking pretty crusty, but when I removed them, they were still quite solid. I realize that a Ford truck has a totally different engine compartment, I was just commenting on how badly the stock logs choked power, even at low RPM on a basically stock engine. Regarding FPA headers, although Stan has them made by an outside source (In the USA!), that does sell their own line of headers, the FPA headers are not available from that manufacturer, as they are exclusive to FPA. I know the 61 thru 66 TBirds have very little room between the towers, possibly even tighter than a 67-70 Mustang or 66-69 Fairlane, especially with the 2 bolt exhaust pattern,and I have never installed a set in a TBird, but I do have the FPA headers that are made specifically for the 57 thru 59 Ford cars with FE engines, in my 59 2 door sedan, and the quality is very good. Nice thick flanges, which are available with either the 8, 14, or 16 bolt exhaust pattern, and with either the higher or lower factory exhaust port location. I am not aware of any other header company that offers that. The mainstream header companies usually slot the upper bolt holes, and either don`t know, or don`t care, that FEs have several different exhaust port configurations. The FPAs are not "off the shelf" headers, you have to order them directly, and tell Stan which style of heads you are using, and then the headers are made to your application. Mine took about 3 1/2 weeks to arrive after placing the order, they even have my name stamped into the flanges. Certainly not cheap, compared to the mass produced headers made for much more popular vehicles. but as far as I am concerned , it was money well spent. Most of the FPA headers are very low volume, not very popular applications, that nobody else makes headers for. I am thankful that FPA was able to service this niche market.