I have an itch at the back of my brain that says that with working scale sailing models, the sail plan is often scaled down. But I stand to be corrected.
If so then not only the sails, but also the masts and spar lengths will also be scaled down for working models, as compared to actual boats.
The other thing to consider, is that unless you are aiming at copying a specific (named) boat, the masts, sail plans, and rigging often varied between boats. As Jonty suggested, taking measurements from the Sarik plan will probably do it. You don't need the plan, you could take measurements by scaling off from an A4 print. If you are unsure how to do this, then there are tutorials for taking measurements from photos online. Using your 34" as your reference measure, this should be straight forward.
