SCCA classifications/events

[jackr@internet.kronos.com]

     I have been browsing the web and found unofficial SCCA pages 
     (http://www.wizvax.net/rwelty/scca/).  I've sent email to the listed 
     contacts looking for information on joining but as of yet have 
     received no reply.  I gather from the Oooooww..di thread that there is 
     considerable SCCA knowledge/membership out there, so here is my 
     question:
     
     My 84 4kq needs new tires.  I was going to buy new 15" wheels and put 
     a 205/50 tire on it.  However, from the SCCA web pages, it looks like 
     putting the non-stock wheel size on the car moves it out of stock 
     class and into street prepared class.  Is this true?  Am I stuck with 
     my 14" wheels if I want to compete in SCCA autocrosses and stay out of 
     any advanced classes?   (I'm a newbie to competitive events.)  If so, 
     does anyone out there recommend a particular 14" tire that is an 
     improvement over the /60 stock aspect ratio?
     
     I've been to the Watkins Glen and Lime Rock quattro club events (no 
     flames please) the past two years, and I... need.... m'm'more.......
     
     Any advice on where/how to satiate my need for a speed/g-force fix is 
     also appreciated.  I live in Massachusetts near Boston.
     
     Jack Rich
     84 4000 Q
     88 Corvette convertible
     90 V8 Q