A patent application written by James Lansdowne Norton in 1919. It describes a balance lever and valve springs at the position where you’ll normally find the pushrod check springs on your vintage OHV Norton. In the invention, opening of one valve puts more pressure on the other valve resulting in that valve to seat more strongly. A further benefit as described is that the valve springs would be remote from the heat of the cylinder head, in a period when valve springs were still prone to break.
Does it work? Perhaps, but problems with valve springs were overcome by use of better materials and longer springs and further, the construction looks rather complex to me compared to the normal setup. It would be interesting if someone could give it a try though!