My gas gauge needle sits all the way on empty and occasionally jumps rapidly to mid level and back down again. I suspect I need to replace the fuel sending unit. There are some replacement units that are the traditional “float on a lever” types and then what looks like the newer “float rides on a shaft” types. I was considering the shaft types. However, I don’t know 2 things... 1. Do I measure clearance in the tank and subtract an inch for total shaft length? Maybe just subtract 1/2”? 2. What resistance range would my original 1989 Carver gauge need? 240-33ohm seems kind of standard when I look at replacements, but how am I to know? Anything else? Thanks!