I put a 396 in my '62 Impala many years ago, but did not go with Power Steering. The car never had it and I left it that way (I'm a no PS fan anyway, lol).
My only suggestion to you would be to go back to the original type PS Steering Box and original '61 PS components. Hopefully that will work with your Big Block Brackets. But pre-measure it all first to make sure, if you decide to go that route.
By the way, my 396 was a '67 as well. A 325 Block with a 375 Solid Lifter Cam, Edlebrock Hi-Rise, Holley Dual Feed and Hooker Headers. Had an M-21 Muncie 4-Speed behind it.
Keep us posted on your progress.
-Parting Out over 75 '58 to '73 Full Size Chevy Cars-
-National Impala Association
-Vintage Chevrolet Club of America