The gist is that if you were to drive by and yell the spot at most stations they'd figure out a way to get it on the air. The downside is that your mix is not going to be aired in the manner it was "finished"
Generally: juts make it sound good, don't overcompress, keep dynamic range tight but don't bother with the loudness wars.
Please note: When commenting on someone's question or answer, you will not receive notification on follow up comments unless you are mentioned with @Username. So for Andrew Spitz, you only need to use @Andrew
This is a very good article discussing mixing norms. Radio norms are discussed about halfway through the article, a few paragraphs after the section headed Peaks vs. Average levels. Norms seem to vary from country to country so it'd be well worth checking what they are in S.A.
I have had different specs depending on what channel my work has been shown at, but generally the specs used by Swedish National TV (SVT) have been functioning practically everywhere else too.
That specs was, as I recall, an upper hard limit on -6dB and a nominal level of about -12 to -16dB SPL A-Weighted. There are many more than that, but the rest of 'em are more or less about keeping an even quality of the material.
Frankly the SPL didn't seem all that important as long as it's within reasonable limits, I only brought my SPL-meter (a Dolby Meter 2-plugin) just about a year ago and worked all by ear before that (actually mostly do now too, but it's good to have a clear reference of where you are!), just being careful not to let it be too low.