The Heritage Commercial article mentions that some Haulmasters came with the incorrect radiators fitted, many of ours were like that. I think that Gardner engined ones had four row rads as they ran cooler and the Rolls six row, most Rolls ones we had came with the four row (although we didn’t realise until the ‘memo’ arrived) so Foden supplied new six row cores for them. A simple task, remove the rad (eight 3/8th nuts) and unbolt the top and bottom tanks and remove the ‘old’ core and fit the new ones. Easy when the truck is relatively new of course! 
Pete.