It definitely looks like a model 1000, here is link to tech manual below.
http://www.alliedcp.com/pdf/manuals/Hopac/1000_techman.pdf
That model can come with a 12, 18, or 21 gpm motor, but most have the 21 gpm motor. And you will need a return line to the tank and not through a valve preferably. So I don't think your thumb circuit will work.
I got the hydraulic kit for ours from Allied, very good kit complete with tubing bent to fit the specific machine, valves, fittings, etc. And it was a lot cheaper than the JD dealer. If I remember right I think I paid about $1800 for the kit plus another $500 to have it installed. Also my kit came with a flow control valve with 3 settings so I can turn it up to 30 gpm for our hammer.
http://www.alliedcp.com/products/install.asp
Other good companies for kits made specifically for each machine.
HKX, in Washington
http://www.hkx.com/cms/
HCT, in Georgia
http://www.hctkits.com/
Forgot to mention: Nice that it has the VMS vary mount system, so that it can be adapted to different machines. Did it come with all the pieces for the mount?