You can do it much cheaper than that kit!! ~$15 for the coupler and ~$5-10 for the gauge.
As to what coupler you need, I'm pretty sure the BX25 is a Parker 60 series. 1/4" threads. Model H2-62. (I'm positive its a 60 and 99% sure its 1/4")
Id imagine the L has a larger coupler, in that case the BX coupler in the set wouldnt work anyways.
Best thing you should do is go look at an existing coupler on your tractor, it should be stamped with what size it is. Then get the same and make your own gauge setup.