Thanks WK. The pressure is spot-on spec, which has me practically doing cartwheels down the driveway. When Dad finally got the tractor running, we pulled the lever on the hydraulic reservoir and... nothing. Tractor didn't even change tone.
It was reeeeeeeeally low on oil. We put about a quart in after trying it once, and it still didn't work, so we just left it go and got back to tinkering on other things. Hydraulics are pretty much the last thing that we hadn't tinkered with.
After the third quart last Sunday, the pressure jumped from 300 to 600, then 600 to 1000, then 1000 to 1250!. The engine grunted, and the familiar squeal of a relief valve... That was a $600 load off my mind, for sure.
BTW, I found out that the top port is the main, and the bottom is the delayed. So, I got the right one.