Originally Posted by vpiuva
But like Cyclotoine said, stack height is going to be your biggest issue.
I'm thinking this is probably not going to be an issue. The current headset is Shimano 600EX series. These were road headsets and had stack heights of 39mm, which is fairly tall. A modern Chorus is 36.5mm. So, provided he has enough engagement with a 600EX, a modern Chorus should provide more and may even require a spacer. But it would be advisable to measure.