Temperature gauge sensor/'70 pickup

[grega57]

I'm replacing the old standard dash with a refurbished gauge cluster. The old unit just had an idiot light for temperature. The new one has a gauge so I had to change the sensor to one that talks to the gauge instead of the light. My problem is that both O'Reilly and Advanced Auto both sell a replacement sender that is too big for the port on my 1970 Chevy Pickup. It has a 307 which I guess is suppose to use the same size as the 350. Does anyone know why these parts stores are selling a unit for this engine that isn't the right size? Where can I get the right one? Thanks, Greg.