My 5.9 into '68 Dart swap
Well I got the header to steering box clearance issue worked out. I took a multi level approach to get the clearance I needed.
First I fabricated an 1/8" thick spacer to go under the drivers side mount, hopefully pushing the engine just a bit towards the passenger side.
Then I did some creative shaping on the end of the steering column with a dremel tool and a stone.
Finally put a small dent in the header using a very long punch and a hammer.
The combo of these things got me about 3/16" clearance.
Here's some pics. First pic is the area where it was hitting.