Hey Keith!
Since I'll be running power-steering off the hydraulic pump's 'priority' port, I won't be switching this pump off! :-}
The drive belt will most likely be a toothed-belt arrangement (like timing belts and harleys). My initial plan is to use a 30t (3" diam) engine sprocket and a 56t (5.6" diam)sprocket, and an 8mm-pitch 20mm wide belt, if I can find the right length, a suitable belt tensioner and deflection sheave. If not, I'll hafta go with larger sprockets on both ends... like a 32x64 combination with an 880mm belt. I'd prefer the deflection sheave, because it'd allow easy on-off replacement, no fiddling with the pump mount, and allow more tooth-contact ('wrap') on both drive-and-driven, with less sprocket diameter.
So, there won't be a clutch function for the hydraulic pump. The mounting plate, however, will only be 1/4" thick, and I'm contemplating the possibility of mounting the clutch AHEAD of the sprocket, perhaps to find an auxiliary function... not a high priority, but I'm always considering possbilities!
...But if you'd like your clutch back, you're welcome to it- it's served me well as a sizing pattern, and I don't need a 'working' clutch to get hole locations and sizes.