How can you tell if a brake lever is suitable for side pull brakes?

Building a single speed bike using parts laying around, Good paint on the old girl so i thought what the hay?!

Built the rear wheel around a coaster brake hub and want to fit a front brake flatbar type lever on the top of the dropbar. Looks like i need a short lever, i know i've got the right one, got a box of them... but how can i tell the difference between short and long pull? Can you tell by comparing them or do i need to take some measurements?