My k frame was modified for use with a rear sump pan. Was not a big deal at all. If you are going to be dropping the $$$$$$ for a HEMI a set of custom headers should not be a deal breaker. Have spoken with a shop that has built headers for a lot of the SS cars......he is using 2.5 (I think that is what he said) diameter pipes. Told me takes no more than half an hour to get them or out, keep in mind this is with the oe k frame/torsion bars/steering box. When you are willing to spend the $$$ on GOOD stuff a lot of your typical troubles go away....But I am sure you already know all of this........It is obviously not your first time down this road......