Those early A bodies have virtually no room( engine bay) for headers ( even the TTI ones suck to install ) on a small block. Or much else
Can’t imagine working on one with a big block, no room for nothing unless you chop up the car.

69 Dart GTS A4 Silver All steel, flat factory hood, 3360race weight
418 BPE factory replacement headed stroker, 565 lift solid cam
Best so far, low 10.30’s 1/4
1.41 best 60 foot
6.56 at 104.17