help on water pump 90 f150

i have a 90 ford f150 the water pump went so i got a new one and it was the wrong one so to make a story short i cant find a water pump to fit my motor, it seems like it had the motor replaced with another 5.0 302 so how can i find out what the motor is from to get teh right water pump.

get the # off the block and look it up online to find out what it came from and year