Half the world will probably say no including every tyre place you speak to but in reality it'll be fine, Monkey ran (I thnk) a BT90 rear and a really nasty front (or vise versa) and still scraped his pegs first time ever on the track.

But of more concern than slightly mis matched tyres why are you called Sue, George?
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Please do not PM me technical questions, if you can't find it on the Forum start a thread