I have also bought sails for my 1988 Sabre 30 mark III from z-sails. They did a good job both with their product and service. They did, however, cut a 159%
jib instead of the specified 155% because they used the measurements from a mark I. That could be indicative of a common lack of attention to detail or an isolated mistake. Either way, if you go with z, specify you have a mark III.