Radial tyres for Somerset

Hello,

I intend to change over to radials on my Somerset, starting with a pair on the back wheels.  I can’t find any positive recommendations about size, especially aspect ratio in recent posts  Any advice would be very welcome.  I recall back in the day when tubeless tyres were introduced that garages blithely fitted tubeless valves to wheels which were intended for tubes and I don’t remember any mishaps.  Maybe there were special valves intended for the changeover period available at that time?

JAC.