There was no fuel gauge on my P-33-1 and I never really felt the need for one. The A4 seems to burn just under 1 gallon per hour no matter what it is doing so fuel level was a simple thing to figure. My fuel fill was in the middle of the cockpit sole and the fill pipe went vertically down to the top of the middle of the tank so it was easy to stick a graduated wooden sail batten to the bottom of the tank to check the level. Most of the last years I owned the boat it was only used for racing so the tank, against conventional wisdom, was kept nearly empty to save weigh in the aft end of the boat. Don't know if it had any positive effect but it was one less excuse for doing poorly. Once in a while I'd fail to measure the level with predictable consequences. Fortunately the boat sailed well (some say due to a favorable rating) so there was always a competitor following me into the harbor who could "rescue" us.
During the time I owned the boat the engine stopped on 4 occasions. Once due to a bad condenser, and 3 times due to wanting to win races (empty tank). On a 5th occasion I returned to a mooring to wait for the fuel dock to have space for us. When I restarted the engine to power 100 yards to the fuel dock the engine only ran half way there before it stopped. I though it was due to no fuel but my 2 year old son appeared in the companionway with the ignition key in his hand.
If you do install a fuel gauge make sure you calibrate it to show when the tank will no longer draw fuel. Having it read empty when the float is resting on the bottom of the tank is well after the engine has stopped drawing fuel. Better to have it read empty when the pick up is still well immersed. Carry some fuel in a jug until you get the calibration correct. My P-33 had about 2 gallons left when the engine stopped drawing fuel in calm conditions (tied to the dock). That's 10% of the 20 gallon total.