One thing in favour of a bench breakin of a ringed engine is that the idle responce will improve during the break in. Fewer dead sticks.

One myth seen on this thread. "You can't hurt an ABC running it in 4 stroking." []

Well that might be true if this keeps the piston and liner at their designed operating temperature but as this is not likely you will wear out the engine in a few runs.

The speed/pylon merchants often use a cylinder head temp sensor on ABC or ABN engines when running in to keep in the right temp band.