I have a 1924 clawfoot tub with legs that have two different casting numbers inside the legs. Two have "43" and two have "43L". I have inspected them carefully and can find no differences. I have put them in all different configurations around the tub and there is always an imbalance, as in opposite corners are too high and too low. The tub rocks.
What Kerwin has are the feet from an (American) Standard Sanitary Manufacturing Company (Mfg. Co.) 5’ roll rim claw foot tub. These were made by the tens of thousands during the 1920’s and 30’s and are the most common type of antique claw foot tub found today.
The feet, in fact, are slightly different. The feet marked 43 should be on the drain end of the tub. The 43L feet should be on the end furthest away from the drain. The L stands for “long” and puts the tub at a slight angle in order for the water to run into the drain. A cross section of the claw foot tub foot appears below:
If the tub continues to wobble, you can be truly "vintage" and use the standard leveling “kit” from the United States Mint – pennies, nickels or dimes wedged under the feet. Yes, this really is the way to level the tub because the feet are not adjustable. When we used to remove claw foot tubs from old buildings we would always find coins under the feet. This is the only solution we know of for leveling old tubs.
Sanitary Claw Foot Tub Feet