You can only approximate. Jets are cheap, kits are expensive. Why risk blowing up you kit over 25 bucks (You can get 10 jets from treathq for about 25 shipped). Check out what other people are running:
http://spreadsheets.google.com/pub?key=p_Ysahl1B79WHMUBbvCzNfg&gid=7
Then buy a range of 20 sizes in even numbers (70, 72, 74...90).