Rolf.
I drove and Ariel Square Four back in the early '60's..It belonged to my buddy and I had just bought a news 1964 Honda 300CC Dream..it was a beauty and of course my buddy wanted to drive it ..We switched bikes and it was a heavy brute compared to the Honda ,but it had lots of "GO"!!!
It sounded like a motor cycle also..
But I would rather have my Honda..still wish I had it..
You should contact the Ariel Club..they will be a great help in your restoration..Here is the link..
http://www.arielownersmcc.co.uk/index.html
Keep the pictures coming..