Correct. I added A-3 heads to a stock block in 1990 and have been driving the car with them ever since. The carb will move up about 3" & back 2-1/2, requiring a BIG hole in the engine screen. The exhaust moves up 2-1/2" and sideways about 2" on each side. I adapted a set of normal GTS headers to my engine. The exhaust bolt pattern is different, too, so redrilling & extensive porting was needed. I also had to physically shift pipe #6 inward with a torch & a hydraulic press to miss the fuel tank (I still had to dent the tank & shield for clearance after moving the pipe & the tank outboard as far as the tank-mount allowed). Then, because of the outward movement of the high-exhaust ports, both collectors ran into the rear springs. I cut a pie-shaped wedge out of each collector, bent & re-angled them inboard to miss the springs & shocks. That meant I had to build a new exhaust pipe for each muffler to connect to the reangled collectors. At the time, no one made such headers; now, Hall and a few other vendors make such on special order, in stainless, even! My way was a h... of a lot of work but it was the only choice at the time, these being pure racing heads never intended for an production car. Note also that A-3s are thicker than 4V heads so you need 1" longer bolts or studs just to fasten them on a block. Hopefully, the set you found is complete; otherwise, figure on about $800 more per head for the needed parts to put bare castings on a 351C.
