1995 G20 Chevvy Van - no temp reading

Discouraging Sunday. Bought universal guaranteed fit NAPA mechanical temp gauge kit. Opened up doghouse, drilled firewall, and..... bushings don't fit! &)(*&)&*. Put it all back together, and still no
gauge reading.
Possible wrong sensor (sender)? It has one wire. Seems to be 3/8" pipe thread, located on left side of engine. NAPA's rig had 1/2" fitting. NAPA's setup requires use of bushing that has shoulder inside to stop sensor from slipping completely inside.
What should the cold resistance be for the sensor? Is it possible the sender/sensor was wrongfully replaced a couple of years ago - never worked....... Are the sensors different between 305 and 350?
I believe engine is 305, not 350. Door plate says it's a G21-305
Appreciate any help - don't want to remove doghouse again without a fix!

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