I have a hard time keeping my 1940 Kohler Wellworth upright when the tank is on the bowl. The tank is just so big compared to the bowl. Out of all the Wellworths I've had, only the first generation Wellworth has that problem. Did you lean the tank against a wall or have some kind of support for the tank?
I had a 1941 Kohler Trylon that had that problem also. Other than that Trylon, my forward trap toilets are all low tank with an elbow connector and I don't trust the elbow alone supporting the tank without securing the tank to a wall.