Norm B. It has been a hectic weekend and I apologize for not clarifying things better.
When converting a non ported pump to a ported pump or when simply taking a 15U Series pump apart.
ONE ... Build a BOX or something to hold the pump so that the aluminum housing rests inside the box and the cast steel part is positoned facing upwards.
TWO... THOROUGHLY CLEAN EVERYTHING on the pump so that no contaminants will enter the pump during diassembly.
THREE... Once the pump is placed on the framework built to hold the housing. REMOVE the bolts that hold the two housings together. Lift the top casting piece from the aluminum housing. It is now possible that the valve plates may fall from the top housing so be aware of this when removing so that the valve plates aren't damaged during the removal process.
<font color="0000ff">You need not worry about any springs or pieces flying out and surprising you and leaving you wondering where they go when separating the two housings.</font>
FOUR... Remove the old gasket material that is left between the two housings. Since you have the pump separated you may wish to inspect and replace any other seals or gaskets that you deem necessary to avoid a future teardown of the unit.
FIVE... The difference of the two cast housings that are the makeup of a ported or non ported hydro unit lies within the housings themselves and if you view schematic drawing fo the hydro units you will see the differences. (Thus what I have written in blue just above this.)
SIX... Install the gasket on the aluminum housing. To HOLD the valve plates in place on the ported (or non) ported top housing use grease or vaseline on the bottom sides of the valve plates. To tell which valve plate goes to the pump and which valve plate goes to the motor. VIEW BOTH valve plates and you will notice on the grooves that one valve plate has two smaller lead in grooves and the other has one smaller lead in groove that points in the CCW direction. The valve plate with the TWO lead in grooves is for the motor. The single lead in groove is for the pump.
SEVEN... After joining the top and bottom of the hydro unit togethr , re-install the six bolts and torque to spec.
EIGHT... After re-installing the 15U on the transmission remove one of the check valves and pour oil into the hole while slowly turn the drive shaft. This will help to prime to system.
Now a little more about the worrying of springs flying all over when disassembling a 15U. The only time those springs would be a worry is when you remove the implement relief or charge springs. You need to be diligent when removing those springs and check for the shims will be inside along with the spring.
If by chance you should happen to take the cylinder block kits out during disassembly it is best to try and keep them separate so they may used in the same area they were used in however both are interchangeable so if you do forget which went where the unit will still work even though there is apossibility the pump clock kit may be switched with the motor cylinder block kit.
I could go into further detail about NOT taking the cylinder block kits apart unless really necessary since the chances of when putthe the pistons back inot the same holes within the cylinder block are slim and the pistons have overtime and usage worn into the holes, I am trying to keep this simple.
I hope this helps and explains things a little better. (If I recall correctly, I did a similar write up a few months back on converting a non ported to a ported hydro. Maybe someone will do a write up sometime and that will be put n the FAQ section as a reference.)