Having run various engines in all sorts of partial assembly, what you want to do is a non issue. Loads are low and run time short. It is good to ask when going beyond normal operation.

First, a diesel runs lots of air through the cylinders, this provides cooling. ( and is why idling a diesel for long periods is a bad thing as it causes incomplete combustion / wet stacking.) Some gasoline cars deactivate fuel to cylinders allowing air to pump through when coolant is lost.

Second, A full cooling system when cold is a huge heat sink all on it's own even if coolant isn't moving.

Third, At some point a thremo siphon effect will occur circulating coolant. ( However some systems might not thermo siphon due to rad hose / thermostat configuration. )

Fourth, think about what happens when a belt is thrown with a hot motor when driving down the road. The fan will windmill for a while but will slow as road speed falls off. There will be much more at "temp" engine operation than a cold start across the yard.

I've run engines with zero coolant farther than the distance you are wanting to. When running sans coolant I pull the belt to prevent overheating the water pump seal.

Just insulate the alt wires ( a rag is fine )