temp guage- need help with correct sensor

[knightowl73]

Ive been trying to get the temp guage towork in this truck since i started driving it and no luck. I thought it was th eguage , so i swapped it for the one from the original 73 truck that the motor came from, but nothing. then I bought the temp sensor that goes in the head for the 84 with a guage, but the sensor is too big. the heads are 87-up and the hole is smaller.

Now i want to put the other guage back in so the scripts are all the same , but i dont know what guage sending unit that will work and fit. anyonehad this prob before? I have centerbolt heads and i dont know what ohms or anything the original 84 sender was supposed to work between so im lost. all i know is that it works off ohms and grounding the wire only tests the guage to see if it moves, and it moves then, but never when hooked up to any of the 3 senders that i have tried.