He's probably thinking of the old HSC 2.3's found in old late 80's tempos and topazs. I don't know much about those engines but they might have a head cracking problem. They are Completely un-related to any 2.3 found in a Ranger. 83-2001.5 Rangers use a lima 4 cylinder in 2.0, 2.3, and 2.5 liter displacement and the 2001.5 to current use a duratech 2.3L 4 cylinder. Neither of these engine families have a history of cracked heads. Not saying it didn't happen to somebody, but it sure isn't common by any means. Seeing Rangers with 4-bangers with 300,000+ miles on them and still running good is common.
You co-worker might also be thinking of the old 2.9L V-6s Ford was using in the Ranger up to 91. Those have a bit of a history with cracked heads.