What steering box was in the car before? The Borgeson is physically smaller than the original power steering box and similar in size with the manual steering box but it is just a different shape, so it doesn't make more clearance everywhere.
It seems to me like your headers just aren't compatible with the Borgeson box, because if you fix one of the things you have a clearance issue with you'll just have an issue with something else. The steering and idler mount on the QA1 K frame can't be raised with respect to the engine, because that would raise the Borgeson box into the engine/headers. The engine can't be lowered with respect to the K frame because that would lower the engine/headers into the Borgeson box. They don't make pitman arms with different drops for these cars, so the only difference in height there would be manufacturer to manufacturer and that difference should be relatively small (not enough to solve your problem). And if they did you'd still need to find an idler arm with the same drop, otherwise your drag link wouldn't be level.
Unless you just have the wrong Borgeson box and somehow there's another one that has a different distance between the mounting holes and the pitman arm. But that would need to be a different case, not just a mounting location difference with respect to the same box, because otherwise it would just move the whole box up or down and that would have the same issue with either putting the box into the engine/headers or the steering linkage into the headers.
So the question is, what headers are guys running with the Borgeson box?
There are some clearance differences between the 68-72 steering stuff vs the '73+, but you'd need to change the pitman, idler, and center link to all be '68-72. That would flip the center link from under the pitman/idler to above them, BUT, the pitman and idler change shape too so the center link itself doesn't change it's location under the car that much. It puts the castle nuts on top instead of underneath, but, it puts the arms underneath so it's just a trade off really.