I'm not sure if it's the same, but I have a real late k and you loosen the two bolts holding the pump_valve unit and slide it down. You may have to adjust the length of the control rods going to the valve too if you move it much.
This is a problem usually caused by wear in the idler bracket pivot area. If you want to fix it right get a new idler bracket (ouch$) and make sure the pivot pin is good. The idler on these two small v belts (they have to be matched) is an special idler. It has a strip of flat metal welded around the circumfrnc. and is heavy. This has to be right to get belts to run. Tention is not all that important. We usually get a piece of heavy wire with a handle on one end and use this to grab the spring and stretch it to the anchor hole.