As far as your NM cows GC's they are ilvl 64 or 67 depending on which cow dropped them. If the cow was one of the unique cows or one of the minions of the unique then the ilvl is 67, that is from the + 3 to the normal NM cow ilvl, which is 64 that uniques get. I too use the NM cows GC's to reroll, I find that you get more GC's per game than what you get in the A3 area. My only problem is I keep running out of pgems, lol, burned through 90 last night rolling a baal sc. Nothing good, best roll was a 19 life with 9 to a individual resistance, cant remember which one though, also rolled a 4 resist all with 6 to life, but kept rolling, looking for one of those high element dmg ones.
Back to the original question you had, the only way to tell the ilvl of an item be it a charm or any other item is to use MH or get someone with MH to look at it for you and tell you what you have.
The only reason to need to know mlvl is to know where to hunt for certain items.
Alvl is really completly useless to know about for the purpose of rerolling charms, so don't worry about that unless you are using cubing reciepes that will change the ilvl when rolled, ie 6 skulls + rare item, or crafting stuff, and I really don't think that you need to worry about the alvl then either, provided you are a high enough lvl to be doing that to start with.
Google