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You'll have to measure the diameters of your pulleys and do the math to determine the actual belt length needed. Once upon a time, I had the math all written up for calculating it but I don't know if I ever posted it anywhere. I still have it at home but I'm traveling at the moment.
An issue with bore adapters is that unless they were carefully machined, they tend to be ever so slightly off-center. I don't think that'll make much difference here if they are, but it's something to be aware of. In the Core-XY designs that wind up fishing line on spools, it's a very serious issue as you get steps/mm values which change as the spool rotates.