The Shimano 105 chain and cassette on my girl friend’s bike are badly worn and need to be replaced. We’ve been given an almost new Shimano ultegra SL triple chainset and we’re thinking of buying the ultegra cassette and chain to get her back on the road with a slightly improved transmission. My question is: To what extent are the different Shimano drivetrain ranges interchangeable, ie. will an ultegra SL chainset work with a 105 front derailleur and bottom bracket and will the original 105 shifters match an ultegra cassette and chainset? Any advise gratefully received before we spend money and get oily fingers!