I had the SSL front suspension kit on both a 1954 Plus 4 and now on a 1961 Plus 4. I'm very satisfied with the combination of supple ride and good handling. It's designed to firm up when pressing on. This seems not to be appreciated by some users who feel that because it is supple over bumps at moderate speeds, it must be too soft for press on motoring. Not so. Having said that, it's a matter of personal preference. Both your preferred driving style and the quality of roads in your area may influence your decision.
The kit comes with excellent instructions with back-up advice from Peter Ballard if required. If you are moderately competent with a set of spanners it is easy to fit because it requires little compression when installing. The compression of the main spring is carried out by adjustment after the initial installation so that the bottom of the stub axle just comes into contact with the rebound spring. It usually requires checking and minor re-adjustment after, say 500 miles.
I have driven a 2004 Plus 4 fitted with the Rutherford spring and damper kit. I found it to be a bit 'jiggly', probably more due to the geometry of the track rods on Morgans of that era which resulted in bump steer. So it may not be a fair criticism of the Rutherford/AVO kit.
You can try my 61 Plus 4 but I'm in North Somerset whereas you are in London, but you're more than welcome. My Plus 4 also has the SSL rear 5 link kit. Very pleased with that too. Not cheap but I'm planning to keep the car for a long time.