In my opinion, it is a horrible idea to move the stock steering box to clear small block.
If you are going with a small block, 700R4, and a modern rear axle, then I will bet a dozen donuts to a dollar (old phrase adjusted for inflation) that as soon as you are done, you will say, "Dang, why didn't go with power steering while I had everything apart?" Power steering will solve the clearance problem.
I recommend strongly, ramshorn exhaust manifolds over headers.
