Sorry dude you are much better off getting a horizontal shaft engine. Too much work to a veritcal to work right. even better, sell your engine and get motorcylce or atv motor. As for free 'plans'. That is next to impossbile. Alot of people have posted what they have done but no real plans or dimensions. But a a couple of sites i liked were
http://www.chriskate.net/gocart/index.html http://myweb.tiscali.co.uk/bennoworld/ It would be better though to just spend the $50 and get a good set. like the set on desertkarts.com
Hope you get it going and post pics to show us your progress