I need to power an irrigation pump via a combustion engine.  I need the pump to turn at 3100 rpm and the engine to turn at 2250 rpm.  The engine will output 58 hp at this speed.  The pump needs 49 hp.  I'm assuming 85% transmission eff. across the belt(s).  Is this a good assumption?

How do I go about determing the best size pulleys and belt size and number of belts needed?  I've never worked with a configuration like this.  I'm familiar with using right angle gear drives and driveshafts only; never belts.

Thanks.