[FWB]

i'm in the same boat. can't man handle the steering at low speed with the fat tires.
i'm going with a Must II pwr rack from NAPA, and a reman Pinto PS pump.
care must be taken with the saginaw as they are high pressure, the Mustang II is low pressure, besides a twitchy feel, you could be getting leaks from over powering the seals all the time.
the pinto pump is actually less of an issue to install as it will take factory Ford brackets and pulley and have connections that are compatible with off the shelf hoses for the pinto and mustang II