The alternative source is a mobile industrial hydraulic pump. like those for plows, lift gates, etc. They assemble to order with either continuous duty motors or intermittent duty motors. I looked into marine out-drive hydraulic pumps, however they are only intermittent duty.
I did find a cheaper source from China, however I wasnt getting the warm-fuzzy feeling as the source made in the good ol' USA.
A rack conversion is not needed Run the pressure side of the pump to the input side of the steering box, run the return line back to the pump - add fluid. Although a rack is cheep, it would be difficult on a straight axle.
The problems we face today can not be addressed at the same level of intelligence we were at when we created them - Albert Einstein Or with the same level of $ - Me