Pity the enquirer hasn't responded. Seems like Massey and Massey Arran were really small players. I found they had a stand at the 1920 Motor Cycle Show but not at the 1924 Show. The Motor Cycle Index lists Massey-Arran for 1921-24 inclusive and gives model details but they barely get a mention in the weeklies of the day. The loud and clear message is they were one of many motor cycle assemblers in the post World War 1 period using all proprietary engines, gearboxes, forks, and so on but like everyone else couldn't make enough money at it to make it worthwhile.
At least this makes for an easy restoration. A 350 JAP engine is a 350 JAP engine no matter what make of bike it is fitted in and the same goes for his Blackburne engine as well. Plus of course they used the usual Sturmey Archer or Burman gearboxes of the day which again makes life much easier.
All in all a Massey- Arran would make a nice change from the usual round of Notron, Triumph and BSA's with the added advantage you wouldn't have the usual teeth sucking anorak coming up to you telling you what's wrong with your bike. You know the sort, "Ooooohh, they didn't cadmium plate the jelly sprocket until engine number so and so, you know, and look, you've fitted the thrumble stick one notch too high!" .
Cheers,