GMC Kid, the concern that you mention above about the bypass always sending coolant to the water pump and bypassing the radiator whether the thermostat is open or not is correct from what I can tell with the NAPA thermostat. The one that Tim showed closes off the bypass, the NAPA one does not.
As Deve points out, it might not matter. It just doesn't make sense to me to send any coolant from a hot engine directly back to the engine without going through the radiator first.
If I could fine a copy of Tim's thermostat, I would use it on my 261. I really like the design of how the bypass works with Tim's thermostat. Without it, I will use a 235 thermostat and housing. I'm not comfortable circulating some hot coolant back to a hot engine by skipping the radiator which the NAPA thermostat would do.
