The type R is probably the most hardcore version impreza. I have seen a few with 555 seats but don't think it's 555 model as such. It has the fabulous driver controlled centre diff.(dccd). Which allows variation of the power between the front and back depending on your driving style and driving conditions. They are in my opinion the best model of classic bar a 22B. Usual things to look out for as per any impreza. Service history, no nasty clunks or grinding from the transmission, smoke from turbo etc. I'm sure there will be wiser people along shortly tho.