The first full blown arranger I saw was by Cavendish Organs just before they went under. I forget the model but was around the time of the TP250 organ. I am guessing around 1986? Silver with on board multitrack midi sequencer (step time or real time) which was unusual at the time from memory. However I think Solton pioneered arrangers with the Disco 64 followed by this:
https://www.youtube.com/watch?v=TYN5dlVqFrI