Stainless Reproduction Fuel Sending Unit photos:
The OEM pickup tube had a tank depth of 16", as depicted in the corresponding photo. The repop's pickup tube has a tank depth of 13" (without the strainer---the OEM was not equipped with a strainer). As such, the repop's pickup tube will require lengthening to utilize the tank's rated fuel capacity. I desired to retain the pickup's strainer. I measured the tank depth in a few locations across the bottom to determine if any tank wall contours would impact the depth possible of the larger diameter strainer. I also desired to have the strainer parallel with the tank bottom, which would allow the actual pickup tube inlet be deeper into the tank, achieving more usable capacity. The tank depth measured 15.25":
I fabricated an extension for the pickup tube from 5/16 steel line. My preference would have been to utilize an inverted flare coupling. However, as the repop was constructed from stainless steel, including it's pickup tube, the stainless would have been too much for my inverted flare tool. So I utilized a compression coupling:
Float Arm & Rheostat
I had placed the repop unit over the OEM unit and compared the float arm length and arc. They appeared to be equal or nearly equal. So I moved on to calibration of the float arm/rheostat. The first step was to establish benchmark resistance readings that corresponded to the gauge itself. I did this by connecting the sending unit feed wire, from the gauge, to a resistance thumbwheel decade box. This box would allow me to dial-in resistance levels with a 1 ohm resolution. Please bear in mind these measurements are likely unique to my truck and may not exactly correspond to yours. This, in part, would be attributable to the fact I had replaced the mechanical voltage limiter, integral to the fuel gauge, with a solid state, IC chip, 5 volt regulator. The mechanical voltage limiters are known to fail with age.
Decade Box Resistance Fuel Gauge Needle Position
7 ohms Full graduation
60 ohms Empty graduation
95 ohms Needle Resting at Empty Stop
79 ohms Needle half way between Empty graduation and stop
I adjusted the float arm stops, pictured below, with a pliers, so the repop's sending unit rheostat measured 5.9 ohms when the float arm was against the full stop. In this manner, the fuel gauge needle would read just beyond the full graduation when the tank was full. The float was approximately 3" below the upper level of the tank, which would be the full fuel level of the 23 gallon tank, with the internal expansion tank. This same float position could be utilized for standard tank. It would just have a couple gallons more fuel to consume before the gauge dropped below the full level.
I adjusted the empty stop so the float would drop lower and the rheostat measured 79 ohms. This still left some reserve capacity once the gauge needle quit moving with a further consumption of fuel.
The gauge graduations will not correspond to tank remaining capacity. This is because the sending unit rheostat has a linear taper. However, the fuel tank shell narrows from bottom to top. As the upper portion of the tank is narrower, the gauge will level will drop more quickly, compared to the lower portion of the tank, for a given rate of fuel consumption. For example, the gauge read just above a half tank when I filled up this morning. It only took 6 gallons to fill the tank.
I haven't ran the truck out of fuel (yet) to know the actual usable capacity of the fuel tank.
Fuel Sending Unit Outlet Nipple
The OEM fuel sending unit's outlet nipple pointed to the right side of the vehicle. The reproduction fuel sending unit's nipple pointed to the left. So it will require a longer length of connecting hose, as depicted in the photo below:
The rubber O-ring, tie wrapped to the float, is to dampen what would otherwise be a clanging of the float against the tank wall, with fuel slosh.
Thank you for taking the time to put this all together. 
