The load-sensing proportioning valve attached to the chassis? I've never seen an actual booster mounted proportioning valve on a pre-90 landcruiser, just pictures. But the lines on Hiluxes are tough to remove once the prop valve is taken off the booster as there is little to hold on to. Be sure to use a flare nut wrench (5 sided wrench, what do they call them Down Under?) as they round easily.