400 hydraulics

I wouldn't bother. Take the power from one of IH valves and send it to your loader valve and back. To operate the loader, the IH valve will have to be "on". I don't think IH provided a detent for those valves so you will have to hold it back with a bungee cord. BTW, select "S" on the IH valve. It stands for single acting. Failure to do so may wreak your pump or motor gear train depending on how the hydraulic system and various relief valves are set up. If this is too much for you, get the diverter valve. It is a no brainer.

Best of all is to use the side outlets on the tractor if you have them. There is a set on each side near the belt pulley gear box. One circuit lifts the loader and the other curls the bucket. You won't need any additional hardware. Find a IH manual for loaders that fit your tractor. It might be model #33, Not sure on that.

The reason for using single action is to prevent pressurized fluid from flowing backwards into the aftermarket valve. If the relief valve has a "pilot" circuit, there could be a problem. YOu might not run it backwards, but someone else is sure to do it.

BTW, I forgot to say that "selector" and "diverter" valves are the same. Catalogs will use both interchangeably.

Both of my 400s have the mid-tractor hyd ports. YOurs should as well. This makes them pre-plumbed for loaders. Use them and save yourself some money.