On the subject of handling of the 4, any handling issues can be sorted by sorting out the suspension. The front damping is inadequate and the rear is undamped. I have fitted cartridge emulators to the front forks which provide proper, adaptive 2 way damping which is equivalent to any modern bike, and I have fitted friction dampers to the rear. Suitable friction dampers were detailed in an article in Cheval a few years ago. The friction dampers are 2 way damped, and surprisingly need very little tension to be effective. The bike has been completely transformed. I have reset the footpegs to give more cornering ground clearance, so now the limiting factor when cornering is the mufflers drag.
Braking, I made a twin leader for the full width hub, fitted and turned oversize linings to fit the drum, which is a big improvement over standard. I never could figure out why Ariel fitted an 8” brake to rear of the MK2 instead of the front. The Rear 8” brake is however as good a rear brake as any.
The square 4 was designed as a tourer and with minor suspension improvements is ideal for that purpose. But the 4 will never run with a swing arm single.