Poly Engine what was good/bad about it and why is the LA better?

One more thing I forgot to mention. Early 273 timing covers had one extra bolt boss about halfway up the driver's side. That's because the 318 poly had a bolt there. 273 didn't, but used the 318 poly timing cover as is. So it still had provision for the bolt that a 273 didn't use. Eventually, LA timing covers were updated to eliminate the unused bolt hole, but I don't remember when that happened.