The Doug’s should clear the manual steering box no problem. I have Doug’s on my 340 and no issues with a stock manual box or the Flaming River manual box which is slightly larger.
The Boregeson interference isn’t totally surprising, those headers were never designed for that box. It also looks like a couple of small dimples might solve the problem, and a couple of small dimples in the headers are par for the course with A-body headers because of the tight clearances and loose factory tolerances.
Are your engine mounts new? If they’re worn out you may need to shim up the engine on one side or the other. Shimming the engine mounts is a fairly common solution to getting the headers to fit a particular car. There are A LOT of threads on here about getting headers so fit different combinations.
The Doug’s should clear factory power steering boxes. But they were definitely not designed for the Borgeson, so even though the Borgeson is overall smaller there may be some tight spots. @BergmanAutoCraft would probably know
