The Roadster you would be considering is the Mustang 3.7 V6 engined Classic variant fitted since April 2018 with 5 link rear suspension. This dumps the leaf springs in favour of coilover damper rear suspension with the then necessary upper and lower links each side plus lateral panhard rod to hold the live back axle very firmly in position. Lower links and panhard rod are available after markets on the Plus 4 but you would still have the less compliant leaf springs. There are further options on the Roadster in the form of dual rate rear coilspring damper package offered by
SSL, with matching dual rate front setup suitable for all in the Classic range. For the Roadster this allows greater improvements in both comfort and handling front and rear making this car with its excess of power IMHO the cream of the tourers in the recently defunct steel chassis Classic range. Possible exception would be a Plus 4 with SSL's own aftermarket 5 link rear.
On the negative side the gearbox ratio's on the six speed Ford gearbox are a little too wide for the Roadster dictating a second gear start under most circumstances and a change down from the economical but very high sixth gear when overtaking at motorway speeds. This gearbox is also physically quite wide requiring a matching transmission tunnel which limits footwell width for both passenger and driver. The equally crisp Mazda MX5/Miata five speed box in the Plus 4 allied to its lower weight helps make it a more chuckable drivers car especially as there are no concerns over throttle lag as found by many owners on the 3.7 V6 engine although you quickly adapt to it.
If you're not in a hurry to purchase it might be worth waiting for the very recently released all new Plus Four on the aluminium chassis CX platform with wishbone suspension all round, the BMW turbo four cylinder variant of the Plus Six. Assuming this would eventually be available in the US it offers Roadster performance with modern handling and both manual and auto transmission.
