Rounding off would be the best solution, making it as close to the New Style as possible. On my Older Wagons I make up a second Coupling using Plasticard, some Lead Strip as a Weight with a small piece of Brass Rod to mount in the Coupling Housing. Having said that the older ones are a bit of a problem to uncouple by the "Hand of God" method due to the Stronger Metal Springs. So they (both Vans) are permanantly put into my Passenger Trains as a Centre Guards Riding Van as was often seen on the Selktalbahn in DR Days.
JonD