Engine cooling issues

[J-440]

Evening all. I have a SPAL electric fan with a 180* switch that turns on automatically. The switch is mounted on the lower part of the radiator. I also have a 185* t-stat. My fan is not turning on obviously because the water temp in the radiator is cooler than the water in the motor. I know the switch needs to be mounted in the heads but I have no provisions to do that. My other option which I don't want to do is to mount the switch in the block, but the headers are pretty close and the block is shallow and not deep enough for the switch to thread into. Even with an extension for the switch to be mounted in the block, it would jut out too far and hit the header.
So here's my other plan. Do I need to get a lower temp switch (125*??) to have the fan kick on sooner or do I need a different t-stat? Thanks again for all the help.