There was def something similar - and sorry Epicyclic it looked far better and more worthy of your praise . Heath Robinson style with a side cum overlever to cock it and was selling last year on Gstar with paperwork provenance from an old auction sale .
I also remember seeing some B45-3 pump ups that had been heavily customised , and fitted this notion admirably .
Longer under arms for easier pumping , wood stocks , bullpup versions too .. Then some custom made by the same maker allegedly using pipework .
All working Pneumatic pump up airguns with good performance too .
Never did get to find out , I wanted to buy some . Kent or south East based I think .
Mate spoke to him and swopped details then he could not get into his computer and lost all data .