I'm just wondering whether mine was originally supplied as focal-plane only ( I bought it as such) but if they all have the 44mm thread (it's not quite 44mm but very close) I might find an original-fit lens for it somewhere. There's a home-made focusing distance scale for an unknown lens, but I haven't a clue what one would originally have been fitted. I suspect a Zeiss/SK/Meyer 150mm/4.5 or similar.
It does perform well as an FPshutter camera, though; allowing me to use a few of the old barrel lenses one tends to accumulate.