They have. I fitted it back in 2015, but donāt tell anybody 
SSL 5L Morgan Rear Suspension
Ride and Handling Enhancement for traditional Morgans
Our multi-link rear suspension for all traditional Morgans gives a comfortable ride with improved handling and control for touring so that everyone in the family can enjoy it.
Development
As Morgan owners and drivers ourselves we wanted to make our cars even more enjoyable to drive. We designed and perfected our SSL 5L multi-link rear suspension for all traditional Morgans.
We continue to improve the product and it now has Multi-Axis CNC machining of the aluminium alloy axle brackets, a process used for many F1 components, giving high precision, accuracy and repeatability. They also look fantastic as they are hard anodised and the steel work is black powder coated providing excellent corrosion protection.
SSL 5L system and benefits
The SSL 5L system is a bolt-on system available for both narrow and wide chassis cars and completely replaces the leaf springs. It is straightforward to install with full instructions for fitting and setup.
No drilling or welding is required for later cars and it can be fitted to earlier cars with minimal drilling.
It is fitted with tuned Spax adjustable dampers and has progressive rising spring rate and roll stiffness.
The system offers adjustable ride height, eliminates axle tramp and gives improved ride, handling and roadholding.
We recommend that it is fitted by a specialist. SSL 5L Morgan Rear Suspension
Ride and Handling Enhancement for traditional Morgans
Our multi-link rear suspension for all traditional Morgans gives a comfortable ride with improved handling and control for touring so that everyone in the family can enjoy it.
Development
As Morgan owners and drivers ourselves we wanted to make our cars even more enjoyable to drive. We designed and perfected our SSL 5L multi-link rear suspension for all traditional Morgans.
We continue to improve the product and it now has Multi-Axis CNC machining of the aluminium alloy axle brackets, a process used for many F1 components, giving high precision, accuracy and repeatability. They also look fantastic as they are hard anodised and the steel work is black powder coated providing excellent corrosion protection.
SSL 5L system and benefits
The SSL 5L system is a bolt-on system available for both narrow and wide chassis cars and completely replaces the leaf springs. It is straightforward to install with full instructions for fitting and setup.
No drilling or welding is required for later cars and it can be fitted to earlier cars with minimal drilling.
It is fitted with tuned Spax adjustable dampers and has progressive rising spring rate and roll stiffness.
The system offers adjustable ride height, eliminates axle tramp and gives improved ride, handling and roadholding.
We recommend that it is fitted by a specialist.
Hereās a link to a forum discussion about fitting it to a car like mine, a limited edition Super Sport.
https://www.talkmorgan.com/ubbthreads.php/topics/788169/ssl-5l-suspension-on-a-plus-four-super-sport
I also upgraded front suspension with their kit to keep the car balanced.