What Belt to Use??

Well I'm getting close to firing up the new 340 for break in and I am in need of a belt to drive the water pump only. I will not have any accessories on the motor and I will be performing the break in on a test stand. The crank and pump are stock pulleys. I was thinking there may be a "stretch belt" that might be available. I have seen the Accu-Link type belts that might work but I'm not sure if I can get the tension I need. I could always just get the extra parts and rig up an additional pulley if needed but i was thinking that if I could get the "perfect" size belt I could remove the water pump pulley and with some effort reinstall the pulley under tension and away I go with one less piece to worry about during break in. Any ideas??