The threaded gear hanger on the Cyclo Benelux rear end has been sawn off. This was a common thing to do BITD as with the Benelux design the threaded part bent outward and wouldn't work with a Campagnolo or similar mech. A rear mech with an attached hanger will be needed.
Interesting frame whatever. I had an original JRJ 'Road/Path' when I was a lad which, I think, dated from around '52/53. It did service over the years as a track bike, TT bike, winter bike, work bike and I think it eventually fell apart under a mate of mine as he rode it to work in the 80's.