"What's your opinion of a safe smokeless load in the New Model 3s ?"

To get back to the original question after a trip around the world, light smokeless loads are completely safe in black powder-era revolvers. My suggestion would be to use whatever amount of about any fast pistol or shotgun propellant (Unique or faster) that will produce a MV in the 600-700 ft/sec range (i.e., a smokeless load not exceeding original BP ballistics) using as light a bullet as is practical. The early factory smokeless powder revolver loads in the old BP calibers used Bullseye (or something close to it) as a propellant. Of course a chronograph is necessary to work up such loads safely, starting low.