"Central 55 George" is probably the cop's call sign that identifies him. When police communicate with dispatch, they don't use their real names, they use a call sign. This guy is probably assigned to a central station (where the dispatcher is located thus addressing it as "Central") with a call sign of 55G. All police departments vary with how they identify themselves, but usually it's pretty closely related to how the military identifies units. When speaking on a radio system, police and the military don't speak letters. They use the phonetic alphabet in order to avoid miscommunication. So, for example, if a unit, squad car (cop) is 33D1, they would identify themselves to dispatch on the radio as 33 Delta 1. This is done because so many English letters sound similar (b, c, d, e, for example) and it avoids confusion. A 10-85 most commonly refers to being delayed. Forthwith means immediately, so he was basically telling dispatch that he was delayed but was on his way.

I'm not sure on the address format, but I don't think it is likely to be 'in the centre' - More likely at 55 Central, Near George. Police '10 codes': http://spiffy.ci.uiuc.edu/~kline/Stuff/ten-codes.html