The Rolls Royce converted engine for the Spitfires/Firefly was allocated the reference RG30SM-S. There's an Airworthinesss Approval Note for RR's Spitfire XIV buried in the CAA's website that explains a bit about it.
Link:
http://www.caa.co.uk/aandocs/21819/21819000000.pdf
Kind regards,
Rich W