Update on the old Mack.
Turned out the first guy doesn't do enough of these pumps on Mack engines, so he didn't have the tooling to hold the cam and torque the nut for the drive hub. Under his suggestion, called Midland Diesel in Fargo and they were more than happy to help. They got it apart, and found sticky plungers and wornout governor. After an ultrasonic cleaning of the plungers, and a light lapping, they were ready to go. Rebuilt the governor, $1900 and done. Got it back, we had marked the drive gear and cam gear before removal, so getting it back on went pretty well. Since that stupid oil filler tube is directly in front of the timing plug, we used a phone with the camera to see in it to line up the pointer, and the bolts that hold the drive gear to the drive hub ended up virtually exact to where they were.
Primed it, cranked it over with the fuel shutoff pulled until it made oil pressure, again until had fuel at injector lines, and after tightening those, when I hit the key I think it started on the first piston up. Everyone in the shop, myself included, can't believe how good it starts. This engine must either be in remarkable shape, or we got lucky and hit the timing on the button. Pretty good considering you're supposed to have this fancy-ass sensor and light box to do it according to the book haha.