a original V8 water pump has a bushing in it, a model a pump has a bearing in it.
when I got my car it had a V8 pump on it. the guy I got the car from said that the pump had about 50 miles on it. I put about 50 more miles on it and then it was toast!
the bushing went out and it had about 1/4 end play in it and was leaking very bad.
I decided to get a V8 pump from Dennis Carpenter. I had to change the pulley to except the fan, the Carpenter pump had a bigger shaft then the old pump. I had to do this to run a fan. I have a Dennis Cling serpentine belt set up on my car, with his 5 blade fan. so after the Carpenter pump did not work I got a Sniders leak less pump . it works great.