March Pulleys/alt bracket don't matter... I have March pulleys and alternator brackets on my 66 and I use the stock PS pump and bracket with no problems (just get the March 3-groove crank pulley)
And the pumps are actually the same (SB and BB), its just the outer sheetmetal housing/reservoir that differs (and is interchangable).
I bought brackets and tried to reuse the small block pump but it hits the power steering box
The Chevelle BB SWP uses a special set of brackets designed so that the pump will clear the steering box. Since that clearance requires the PS pump to be relocated upward, there isn't room for the "regular" PS pump reservoir beneath the alternator, and thats why they needed the remote reservoir...
I exchanged the 65 pump at Auto Zone for a later remote fill type for about $36.00.
Mark, what application? I know some of the 80's/90's Chevy HD (1-ton? 3/4-ton?) pickups used a remote setup that was similar, but never looked to see how similar (although my buddy has a setup on his 66 that functions and looks stock but doesn't look original "1966". He bought the car with it though)
Most "Chevelle" places sell the correct brackets including GU, You probably can find the outer housing separatly, and reuse your pump internals... Since the pump is relocated, the hoses to the box might not fit right (watch the headers and belts for clearance)... Yes it gets expensive...
Not sure of a cheaper way besides piecing stuff together or going complely aftermarket which is probably more expensive than the "stock" stuff.