We have a lot of old homes heated with cast iron radiators here in Minneapolis and install Weil McLain high efficiency condensing boilers often cutting fuel bills in half. Weil McLain does require primary/secondary piping on all installations regardless need with the implied threat of not honoring warranties, but we have never used primary/secondary on any cast iron radiator system. When converting a single zone gravity hydronic heating system to a pumped system the friction loss of the system piping normally need not be considered. To add a pump would just add to the cost of installation and operation, making the practice not only ignorant, but negligent. Even with two zones as long as the minimum flow rates for your boiler are met and the boiler is not over-sized, the perfect heating system is within your reach. Good for your installer; he is one of the smart guys.