Found! Charlton Comic’s “The Comic Book Guide for the Artist Writer Letterer” in pdf form.
I’ve looked for this particular booklet since I was a kid, I had missed the boat on it back then by about 5 years. I had collected the bagged 3-pack Charlton comics in the late ’70’s, the comics had been bundled after sitting around for a long time. The booklet rarely shows up on eBay. Originally offered in1973 the booklet was so popular it went into a 2nd printing.
Here is some nice history on the booklet, as well as jpeg pages and a pdf version.