Quick at a distance difference between 755 and 855 is length aft of engine side panels. On 755 the engine side panel ends just below the letter R in DEERE. On 855 (and 955) the panel ends below the letter D. I assume the tractor you are looking at does not have those side logos, but this picture should give you an idea of that difference. That length on the 755 is about 5 inches.