I'm glad you asked this as I'm thinking of making a grapple. From what i understand you'll need to add at least one remote. I'm assuming that it doesn't need the "float" feature some of the spool valves have. I'll probably add two valves so I can also add a top and tilt. I'm not sure where you would tie into the hydraulic system though.
Here are some of the questions I have. When people are saying they use a rear remote I assume that they just run long hadraulic lines from front to back, if so where do you route the lines? Couldn't you just make a tee and have quck connects at both the rear of the tractor and one set near where the FEL connects. How do you run the hydraulic lines down the loader arm? Do you just wrap them around the other lines or did you make a braket to hold them but is easy to remove the lines when the grapple comes off?
I haven't priced it out yet but I'm thinking of justifying buying a plasma cutter to cut the steel needed for a grapple. I haven't seen one in person since deciding to do this so I'm not sure how think of steel, how many arms, one or two cylinders, and how big it should be. If I could do it with enough savings to cover part of the cost of a plasma cutter I'll probably do it next spring.