A new engine should be tight, I would be surprised if you could turn it over with the fan and belt. The rear seal is enough to keep it from turning right over. After start up, it should be a lot looser.
Sounds like you have the bases covered. Running on 12 volts is not going to kill the coil or points. In the long term maybe, but not for a 20 minute break in. Have the 6 volt battery all wired in with good quality heavy cables. Jump the 12 volts to it to fire up if needed or just hook the 12 volts right up and forget the 6 volts. If you are worried about the points, change them afterwards. You main concern is getting it started ASAP and keeping the rpm up (1200-1500). The rpm is what oils the cam and lifters. Adjust the timing while the rpm is up, close enough is good enough at this point. The garden hose is to keep it cool, don't be afraid to get it wet. The radiator must stay cool or the engine will overheat which is really really hard on a new one. The cylinders are rough and get hotter then normal along with the crank, rods, and oil. Cooling is second priority after starting.
Use a good quality temp gauge or heat gun (infrared type). Monitor oil pressure and temp all the time.
Good luck, sounds like you are ready!
Joe
