I think an LFZ engine would originally have produced 22 bhp at 4750rpm according to the 1933 brochure.
With a detachable head and block fitted the engine could be either 498cc or 596cc. According to the 1934 sales brochure:
488cc 27 – 28 bhp at 5400rpm
596cc 31 – 32 bhp at 5200rpm
I do not know of an easy way to determine the capacity without removing the block.