Invisible Scarlet O'Neil #3 (Harvey) is marked c2c, but I'm not sure it is.
1. It's 32 pages at a time when 36 was standard.
2. No text pages. The previous issues had 2 one-page text stories & I believe to send a comic through the mail it had to have at least 2 text pages.
3. The interior front cover is b&w, but the next to last scanned page is in color. It seems to me that b&w ifc & ibc's were the norm at this time.
Unfortunately I don't have a paper copy to check against it.
