Yup on the Williams.
The integral valve is double-acting. Based on my limited knowledge of hydraulics, I'm thinking the it is an open center valve as the pump can idle with the valve in the center position. If that's the case, then pressure/heat problems will only surface during actual movement of the piston, IE long enough to raise and lower the bed.
Unless I'm missing something (and I probably am...) I don't see this as a problem.
I'm building this out of whatever I have laying around from years of being a packrat. If it were being purpose-built, I've used a shorter stroke cylinder and a smaller pump.
Not knowing what I was doing, I was worried about turning the pump fast enough. Obviously, that's not going to be a problem. I'll swap the smaller gear onto the engine and scrounge around and see what I can find for a larger gear for the pump.
I also have a friend digging through his stash thinking he may have a flow control valve somewhere.