If you wanted to stay period-correct and bolt pump to a Y-block, the '55 thru '59 Ford and mercury factory power assist system will mostly bolt-on. The only things you might need to change is the idler arm and bracket and the sector arm, which would need to come from a '54 Ford or Mercury.
Your steering gearbox and steering column do not need to be changed to convert to power assist. It is completely divorced from the steering gearbox. That is not true of the Lincoln power steering system of that era.
Every once in a while, you find one or a partial setup on e-bay. Last year, I sold a completely restored/rebuilt setup I had in my garage for many years.