[PNJSNAK]

Dave:
I just checked my motor (351W) location.
The first header bolt on the passenger side is 15-3/4" from the closest edge of the upper crossmember. The centerline of the water pump pulley is 9-1/2" from the top of the lower crossmember.
With the body in place there is 6" clearance from the back of the passenger side head to the firewall.
What might be more of a problem for you is that with my motor in the current position the headers are very close to being centered in the area between the footbox and the inner fender well. On the passenger side there is 1-1/4" from the header to the footbox wall. It seems that you will fit depending on the bends of your headers but you will need some kind of heatsheilding on the footboxes possibly. Or you might need to get the headers rebent a bit.
Jim