This will be a slide-hammer you need. It will also be necessary to improvise an adaptor . The idea is to shock the pump out of the cylinder block with a series of upward blows. I have improvised before now with an MGB engine lifting eye and a shaped piece of steel as an anvil plus a club hammer.
Something like this
http://www.metalnerd.com/cat10.htm
Its at the bottom of the page.
Local tool hire companies are a good bet.
In my early days of 1850 ownership I tried simply lifting it out with the same MGB engine lifting eye and a hoist. I had a lot of the weight of the front of the car on the pump and it still wasn't coming out . I remember tapping the bolt head with a hammer in that state and it suddenly came out whistling past my ear. Very scary ! I'd never do that again.
Jon is the Club water-pump expert. He has done an excellent write-up.
http://www.dollywiki.co.uk/wiki/Water_Pump_Overhaul
Good Luck with it,
Tony.