yeah you can tell from the pulleys. a short pump pulley is about 2 inches tall and a long is abbout 4 (realllly rough guesses) if you were to sit them down on a bench.
you can count the blades on the fan too. bursons know which is which.
yeah they are not interchangeable either, if you get the wrong one, about 20mm sticks over. sabathss has a short pulley on a long pump and you can tell. its chewed off half his belt.