Hi im a firm believer in the free wheel manual locking hubs,they dont go wrong unless abused, the amount of people that have come to me and said 'where can i get manual hubs from cos my autos have packed up', once you lock em in your in 4wd, whereas the autos the half shaft actually has to spin before it grabs the wheel, which in theory means you could already be stuck in some circumstances!! anywho, have you phoned milner and asked them about it, they will tell you whats what, they are a good company with knowledge, i use them alot!!,you could be really cheeky and ask them whats involved etc, then go onto ebay or to a scrappie and get the parts for dirt cheap money,second hand manual hubs cost about £50 a pair, never done a sportrack im a f70 man but i dare say they just unbolt of and bolt different ones back on, probably just also involves removing a wire and tie it out the way - not sure.Give em a ring and probe their minds!!!!!!:p