diffuser/spoiler design

[wolfcri at optonline.net]

Hey Guys,
   I'm in the precess of building a diffuser and a rear spoiler (not a ricer park-bench-style F1 wing) for the NX.  I was just wondering if anybody had any experience they wanted to share, tips to follow, or even plans from one they built...  If not, i guess i'll be playing it by ear.
   The car is going to be raced primarily roadracing at lime rock, pocono, and watkins glen (and if englishtown raceway park ever opens their road course...).
I have no idea what class i want to run in yet.  I dont plan on being too competative for at least the first year.  Probably just do some hot lapping this year to test and tune.  Either way, will mods like this be a problem when i want to start racing? ie. being placed in a class out of my league? Thanks, Jim Kaiser