Yes, this is where you can put on a gauge or sending unit. You just need to get the gauge far enough away from the bowl to fit the gauge in there. Maybe a long L #4 JIC.
Look here for fitting ideas:
SAE 37° Flare (JIC) Hydraulic Tube Fittings
Straight Thread O-Ring Hydraulic Fittings
I do not like the idea of drilling a hole in the fuel filter cap or clamping a hose on the drain valve. I have done them both and the hose on the drain valve kept popping off and flooding the valley with fuel. And the cap gauge vibrated loose when I drove it.