Hi "MYNAMEMF82" I mean please make an effort - really? Anyway back to your question, I don't think you can take the barrels out to 750 but you could rebore them (550) out to max and sleeve them if they are really damaged but that might cost more than the bike, best to look out for a set of spare barrels on ebay or some such and just use the old ones as an anchor. You can't plonk a set of 750 barrels on either as they are designed for a longer stroke than the 550 you would be just throwing your money away, if you really want a 750 then might be cheaper to buy one instead of making your own. Not saying it can't be done just it will cost you more than the bike is worth to do it. Plus your bike has the 550 cdi heads and cams these won't work on the 750 barrels, least pretty sure they wont at least not without a shit load of work. Of course you might be the best mechanic there has ever been and your able to do this on a rainy weekend and the rest of us will be in awe of your skill but as you haven't said "Hello" in the New Members section we will never know (hint). It really helps if you say Hello in the new members section as folks are wary of "one hit wonders" of which we get a lot, it's just like saying Hi to a group of strangers who you met for the first time and helps folks know you here for the long haul not just cos your stuck. Just in case, Welcome to the YOC and hope you stick around cos your project sounds like fun and we would all like to see how you get on.