Re 56ac: in my experience a helter skelter is a slide not a ride.
Re: odd words: for 11d, I had to Google very persistently (no, I do not mean to search for Romance) to confirm that the answer was simply a hidden word.
On the other hand, having some knowledge of both musical and chemical terms, 32ac and 19d leapt out at me fairly quickly and sporran and Procurator Fiscal were there for the Scots among us.