Not sure if it has been suggested, but it would be re-bored and rifled to a .338 or .358 calibre on the .303 case - improved or not - your choice.
I'd contact a barrel maker in the States and ask if they do re-bores and if not, will they suggest someone who will.

Ken Waters has had more than one shot-out .303 re-bored, one to a .358 on the .444 Marlin case. I'd stay with the .303 case, myself.