adding radiant heat

adding radiant

adding radiant heat to cast iron hot water boiler with one pump on return and 2 zone valves on feed. what is the easiest and correct way to do this. i fiured i would tie the feed and return together,use existing pump as the primary pump which would run when ever there was a heat call. cut a mixing valve pump and thermomother in to feed for my radiant loop,and place ball valve and boiler drain on return of radiant to bleed it.use a relay to operate new radiant pump. will this work?
thanks eddie