To answer the original question, you need two hours plus a checkride to get the additional HU269 rating.
Are there different rules in non-UK Europe as opposed to UK Europe? I did my PPL (and CPL) in an S300 and did R22 type rating in 5 hours 5 minutes (5 minutes over the minimum). And I'm a pretty crap pilot - never did anything else in anywhere near the minima!!
With 250 hours under my belt when I started the R22 rating, I still found the R22 tricky; twitchy (I had to actually manipulate the yaw pedals rather than use them as a foot-rest), carb-heat (eek - scary), but governor-off training? Hardly noticed!!!
If you can fly an S300, you can fly anything.
With all the hindsight I can possibly muster with my 300 hours experience, I'm glad I learnt first on a Schweizer; it's a cracking little helicopter that will forgive the odd trangression - the R22 might not!
Cheers
Whirls