about 2 years ago,
https://www.whifbitz.co.uk was doing this, they were taking Minis and installing Civic Si engines and trannys, 160hp or higher depending on trim. i couldn't find any stateside shops that were doing this, and Whifbitz had apparently done quite a few and i was told had quite a history with Mini restorations, and i was scheming to buy one from them and have it imported, alas my father who for all intents and purposes was my "bank" at the time, refused to back such an endeavor, lol...
in any event, after checking their website again just now, it appears like they have fully devoted themselves to Japanese->UK imports. oh well.
thanks for that link, the Mini w/ Civic engine transplant is #1 on my list for project cars in the near future, but i couldn't find anyone stateside with experience in this, so it looks like i'll be talking to GoMini regarding that!