Good point. But in the case of my Dakota, its the donor chassis going under my 56 Dodge cab. So far I plan to cut up the Dakota cab, but retain the firewall/floorpan. Then I plan to weld the 56 cab onto the Dakota firewall/floorpan. If I need to create clearance to the firewall I can do that when the 56 cab goes onto the Dakota floorpan. That's assuming something like long tube headers can still fit within the area provided to the 2001 Dakota firewall.

Thanks for those pictures. Are those the long tube headers in a Dakota chassis with the 5.2 Magnum? My goal is a stout, torquey 5.2 Magnum and long tube headers help keep the torque curve lower in the RPM curve.