If you can't find a belt drive pump, you can get a couple of pillow block or flange bearings and mount a shaft with a belt pulley on one end, and a flexible coupler such as a spider coupling on the other, and use the spider to drive a shaft drive pump. (Spider couplings are also called jaw couplings or lovejoy couplings).
Shaft Couplers | Power Transmission | www.surpluscenter.com
Don't give into temptation and use a solid coupler, because your shaft bearings will fight the pump bearings, and you need the shaft bearings to take the belt side load, and a flex coupler will make sure that the pump only sees twist from the shaft and no side load.
Mount your shaft bearings on a mount attached to your engine, since it moves and shakes some in the motor mounts, if you mount it to the the truck frame it can mess with your belt tension. If your truck had an air conditioner, that might be a good place to mount your pump and shaft, and you could use the same size belt.
You will need to figure out what speed you want to run your motor, then use that with the pulley size to get the relative RPM of the pump (I suspect with an AC compressor they run close to 1:1 with engine speed, as opposed to an alternator that runs faster). Once you have the pump RPM, you can then use the needed flow rate to move your cylinders to calculate what displacement of pump you need. By going with a shaft drive pump, it can be a little easier to swap out different sizes of pump, as long as they use the same size and type of shaft--there are several (plain keyed shafts, splined shafts, and tang drive). Keyed shafts are probably easiest to work with.
I suspect your radiator is in the way to mount a flange onto your crank pulley to run a shaft out the front to a coupler and pump, avoiding the need for a belt.
For an efficient truck-size loader, a power steering pump probably does not have enough volume or pressure (but they can sometimes be made to work for a garden tractor).
You likely have the room for a good sized hydraulic reservoir, and could use the weight on the back (was front) to counteract the bucket, so I suspect you can get away without needing a hydraulic cooler, but should plan on having a filter.
If you can, pick all your hydraulic parts to use the same type of fittings. A lot of people like and prefer JIC, but if you are buying surplus pumps, valves, and cylinders they can be pipe thread taper (NPT), pipe thread straight (BSPP), O-ring boss (SAE), O-ring face seal (sometimes called block, I think?) and we haven't even gotten to the metric fittings yet.
There are adapters between most of these, but if you need to buy them for every piece you use, you can quickly eat up any savings you might have made buying the "cheap" part, AND they take up more room you may or may not have to run fittings and hoses.