Anyone know of any adapter that will go between the head & header that has a slight angle to it to pull the tubes closer to the oil pan & away from the frame?

Something like this:

 

Might be better/easier to cut the tubes off the flange and reweld at the angle for the clearance needed?

 

Yeah probably, I had thought that too.

 

Maybe not cut completely off, but cut from underneath near the flange ALMOST to the top.
The width of the cut ("kerf") will allow it to sag a bit, likely enough for what you want.

 

Just a bit more thought as I watch the Viking and Colts battle it out.
Don't how your headers are welded but many are welded on the inside of the header flange towards the cylinder head. Could you die grind out the weld and move the headers as needed and then reweld on the inside? Mod would be invisible.
Oh and the Vikings are trailering by 7 but on the move?

 

How much do you need to move it.

Cutting and grinding or adding an angled flange is overkill for a few degrees.

Bolt it to the head and bend it. If more is required, heat the 4 tubes and bend it. Ratchet strap, chain fall or scissor jack.