Assuming this parts diagram is correct, there is indeed a union 040 in the discharge line.
First, does your loader's valve have six or seven lines connected to it? Also, maybe a picture or two to confirm it has a pressure relief. Lastly, do you have the return pipe 080, it should be located on the transmission case.
View attachment 143092
If you have all the requisites, you would replace the union with two elbows. Then run a line from line 010 to the P port on your loader valve. Run another line from the power beyond (probably N) on your loader valve to the 050 line. Put male-female disconnects on those two lines so that they can be connected together when the loader is removed. Run a third line from the T port to line 080, this gives you a dump to tank. You'd probably want a quick disconnect on it for convenience, but it can be left closed off when the loader is off.