Clivewatson,
A well worded post with sensible questions. To answer some of them:
The Hunter is not cleared for intentional stalling and so 1g stall speeds are not assessed on airtests. Even if they were, the lift curve of the wing varies with Reynold's number, effectively true airspeed, (and Mach number but that would not be relevant below about 0.5M) and so a straight mathematical calculation of an accelerated stall speed at a given g would not be totally reliable. And if you don't know either the g and the speed around the manoeuvre then you cannot calculate radius. Even if someone finds the data sheets for the wing section it would be almost impossible to calculate an accurate theoretical value of lift coefficient for the whole wing. This data may exist in the BAES archives but access may not be easy.
I have never seen a performance manual that deals with looping radius and pilots often have their own numbers for use in ACM or aerobatic practise but these normally are rough figures for guidance and then have a safety margin built in. I hope that this helps a little.