Some good discussions on spring selection for a first gen camaro over at camaros.org.
Sounds like you need to raise it up more than a 1/2 inch. However, if you think 1/2 inch would do it for you, I would suggest a pair of these:
http://www.ebay.com/itm/1964-81-CHEVELLE...r#ht_2095wt_854
I have a pair in my car. Needed them to fine tune. I used a pair of springs out of a big block El Camino, then cut off either one or two coils (sorry, can't remember as i did that in 1977). I still have the original Z/28 springs, but they sit a little high for my taste. However, I can put them back in any time I want. That is why I cut up the El Camino springs.
The 3/8 spacer will take the overall height up about 1/2 inch.
If you need to go higher, I would suggest finding someone who has a car that sits how you like, and see what spring they used.
Good luck.