Again, just for the record if anyone else is trying this.
OK, seems better today. Cinelli cork/gel bar tape, bars angled down less. Saddle moved forward a bit. And no more slipping off the back of the bars! Yeah!
Still not totally convinced drop bars are going to work for me though; feels a bit as though I need either longer arms or a shorter stem. Maybe I'm just too short, being almost at the bottom of the range of heights Sam suggests for this frame.
I should say that aside from struggling with the bars, the bike is lovely to ride. Very happy with it!
EDIT: in case I forget, thanks go to Sam himself, and Roger at Head for the Hills for this bike. Plus a number of people on the classifieds selling me other random bits (including one item which still had the original free packet of sweets and was practically brand new, and another which came with a free waterbottle).