Engine is in...need to shim driver's sideside

I think shimming on the drivers side will just drive the #7 pipe into the steering worse.
shimming the passenger side will allow the drivers side to drop down the slope of the mount to the end of the slot, and maybe gain you some clearance, but it will be minuscule and somewhat tricky.And then you get to deal with the off-level carburetor.
I would loosen the bolts on all the engine brackets and let everything settle to the bottom, then retighten. You might have done that, if you bolted them on with the engine upside-down.
And then I would pull the column and modify that to fit. The usual fix there is to shorten the outer sleeve at the lower end. If the coupler hits the pipe you can replace it with a U-joint.

But above all, like others have said; you gotta insulate the pressure hose from the header. If it ruptures due to heat, you will have a fire there right away.

I thought Dougs were supposed to be the final word on A-body headers?Perfect fit and all that?