If the pistons are not marked with an arrow on top, they will go either way. The rods do matter. The rod correlation numbers go toward the cam shaft, the oil spray hole (lower end of rod) goes away from the cam side.
The pump plate, you should see wear marks from the gears. If the plate is symmetrical and machined on both sides, it can be reversed to get a new surface for the gears to run on. The gasket behind the plate is the critical component. It serves as a shim to set the gear clearance. Should be .007" end play. Also the mount gasket sets the drive gear to crank gear backlash. Should be .005 to.010".