Just came across this on YouTube:
Link to original page on YouTube.
https://youtu.be/QECLiwBCYDg
In this short video a Thai shop tears down an EX250L/M engine and an EX300A/B engine to compare the internal differences side-by-side and rebuild the 250 engine as a 300. As we all know, they are essentially the same bike. It became a 300 for most of the West in that generation but remained a 250 in some markets (mostly SE Asia).
The 250 engine was severely damaged and all the important bits were replaced with parts from the 300. Now someone is rolling around with essentially a 300 in 250 land.