I've done it on an engine stand that I stablized with a 4x4. I ran an 8' 4x4 under the legs of the stand and put a lag screw down into it so it couldn't fall over. Then I put a good grade 8 bolt in the head so it wouldn't turn. After I was done running it I realized that the torque of the engine had worn the bolt almost completely through, so I therefore don't recommend that anymore
For cooling you can put your radiator hoses into a big barrel of water. I should say that 50 gallons should be plenty. Eventually you'll heat the water and have to stop, but you'll have a while to run it. I used a thermometer in my 35 gallon barrel and ran it until the water reached about 160. I got about 20 minutes out of it.