Good point that I can't answer. Big, wide, tall engine that's heavy for its stock displacement! I would do whatever it takes to get that thing down as far as the frame would accept. Swap-shops cut and build box-reliefs into the back edge of Pantera inner rear fender wells for head clearance, and saw off unused lugs etc from heads where they interfere. This is needed especially for post-'80s Panteras because their square-edge inner fender panels seem a little larger than the smooth stamped ones used in '71-76 Panteras. I know of one GT5-S that needed boxes done for a pro 4.6 mod-motor conversion 15 years ago. Most of the extra tire/wheel width in wide-body cars is outboard so there is some room to do this. Changing plugs is easier than on a 351-C!