The towing capacity of a 1987 Chevy K5 Blazer varied significantly depending on the engine and drivetrain options. There wasn't a single number. You'll need to consult the owner's manual for the *specific* 1987 K5 Blazer in question to find its exact towing capacity. The sticker on the driver's side doorjamb might also list it.
Without that information, providing a figure would be inaccurate and potentially dangerous.
