Often, what happens is that the tab on the bottom of the column will hit the header primary pipe for at least one cylinder, stopping the transmission from making shifts into the appropriate gears. The rods and bellcrank can also be an issue, as they do take up some space under there. I had serious interference issues with the column shifter linkage in my '67 'Cuda, until I modified the mounting of the shifting components. I have factory B/E HP manifolds with 2 1/4" pipes, and I was having these problems. I would say that for most headers, the basic rule is correct: no column shift with headers.
