Lionel O-gauge transitioned from latch to box couplers in the mid to late 1930's. I find that the box couplers are much handier to couple and uncouple, and look somewhat better IMO. I've converted some of my latch couplers to box couplers on my small fleet of prewar Lionel.
The different series of prewar Lionel trains don't necessarily look good when intermixed, even though they may run OK in the same train.
