Your correct that you need a 223AI Go and a standard 223 for the No-Go. You can get by with just the Go gauge and use scotch tape on the base to make it a No-Go if you want. But as you questioned how do you know what .004" feels like. I always buy both, set the headspace and then I will try the tape method to see how close it is.

For the extra $25 I just feel safer using both. I do like to set the Go gauge a little tight. Never had a problem closing the bolt with new brass.