Does anyone know if a 74 351w water pump is interchangeable with a 69 windsor?  

I'm afraid not.  The 1965 289 through the 302 and up until 1969 351 pumps were all the same, but it changed in 1970-1978.  If you already have the 70's pump handy, after you take off your 69 you could stick it up there and see, but I am afraid it won't fit.  

Actually I think it will bolt up, Ford made several different timing chain covers but the water pump pattern was the same until it changed over to serpentine drives. The real problem is that the pump is a left hand return (right side as you look at it from front) which is the opposite of the 69 right hand return. 302 and 351 changed over along with 4 bolt front pulley in 1970.  

Thanks for the reply.  Guess I'll give it a try when I pull the 69 out.  

Your 69 most likely has the bottom return hose on the PAX side.  If the return hose is on the driver's side from your radiator then you are out of luck.