You don't have to run it on the bench for two or three gallons. Put it up in the air after you get through this stage as stated by CAP232CM:

"With a ringed engine the idea is to run it VERY rich for the first few tankfulls punctuated by small bursts of leaner running to allow speeds to build up for short periods. This should be carried out at FULL throttle using the main jet needle to control speed changes. After the first tankfull the model can be flown."

"As more running is achieved the leaner periods can be prolonged until about one hours running has been accomplished. The engine should then hold full power without fading. If the engine shows signs of slowing, richen the main needle mixture immediately."

Then be careful not to lean it out completly. Finish the break-in in the air.

Jim