Hi Jonny,
yes give Dennis Allt a buzz at Transimp... he used to have a quick 998 Sunbeam 1.0l when he was young... he runs an imp engine tuning business...
email him on Dennis Allt [transimp@ntlworld.com]
he is in Hemel Hempstead...
other imp engien specialists are listed on www.theimpclub.co.uk/spares/ under spares panel
also might be worth speaking to the local imp bods in your area:
http://www.theimpclub.co.uk/ac/
look under Peterborough
Si