The early A cars just suffer with way too little room for that large 440. I have owned and raced a 65 dart/440 combo since 1981. A lot of work, but the best solution, is a different front suspension system of some sort. A Mustang 2 aftermarket kit will allow much more room. Subframe ties and a simple rollcage plus that M2 front suspension, and you can then build some headers that WILL WORK. The whole reason to put a 440 in an early A is to go faster, and strangling it with bad headers really hurts.
Consider going to a 400 or 383 based combo to get some room. Also study up on what a conversion to a Mustang 2 front suspension will do for you. Putting in subframe connecters is a virtual must to save the body, and the M2 suapension will solve a ton of head aches, including the bolt pattern, disc brake conversion, header room, radiater room, to name some.
