Zero Turn Mowers

I purchased a RZ4621 mower on 10/29/11 last week the engine started to blow blue smoke real bad after only 47 hours of service. The mower came with a 21HP Briggs & Stratton engine. I brought it back to the dealer and I'm waiting for their diagnosis. My question is: can I replace the engine with a Kohler motor and will Husqvarna warrany the change? I'm concerned that a rebuilt Briggs & Stratton engine will not give me the long term service that the Kohler engine would.