Replacing the chain is easy enough.
Remove the old one via a chain splitting tool or an angle grinder (my weapon of choice!) to remove the rivets of one link.
Offer up the new one, and determine how many links you want to keep as they always come to long. Don't know how this works with a 749/999, but on the old 916 models you wanted the longest chain length you could get away with, as this equated to the longest wheelbase...which is a good thing for stability. I guess the same thing applies with the new model?
Cut the chain to length, and then rivet it in place with a riveting tool. Some recommend using a hammer and 'peening' the end over...but I have tried that several times and just find it hamfisted and not good practice. Lots of peeps on here have riveting tools, I'm sure if you ask nicely someone may be willing to lend you one for the weekend.
As for makes etc...you pay you money and make a choice.
From experience, I would recommend Tsubaki HD X ring gold (great price and look good) or the DID all singing all dancing SBK chain (can't remember the name right now)...looks real sweet, but is expensive.
Nelly or Robsom Racing do the tsuabki chains...JHP for the DID.
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