I made 375 Whelen AI cases from 30-06 (35 Whelen cases too). I used RCBS dies. I have most manufacturer’s die and I like RCBS as much as any. Their warranty is outdistancing.
When the case is opened up it tends to shorten. I’d bet the length wouldn’t be an issue. If you have intermediate dies such as 338 you might consider opening the neck in steps.
You could open the neck to .375
And size in the 9.3x62 full length die. Fire form if desired.
After I modify cases such as that I anneal the necks.
