Sadly, I don’t have experience with 1000s of Morgans, but I do know that my plus 4 and many others certainly in the past decade or so, were supplied from the factory with 195/60 15s.
Just saying to set the record straight!
So was I. Gambalunga mentions using two tyre sizes on his Plus 4. 195/60 15s and 195/65 15s. I felt that should be absolutely clear. Heinz picked it up right away.
I seem to have offended some people here again.

CBY. It is a small matter the flatten the ends of a cut spring. Any machine shop or well equipped amateur garage can do it. In fact that is what happens to all coil springs including MMC. I am surprised you are unaware of that. I am very impressed with your credentials. I am merely a retired fellow (32 years) with Morgans.
As I noted a few times, I have decided that that a neoprene bumper, progressive, would be a lot smarter than anything suggested to date. I gather you prefer a progressive spring of varying rates and inconsistent strength along its length. Would that mean you would also recommend a bootie to cover it?