Sprinter Arms used to do rebores. Not sure if they still do.
I think they were in South Aus.

Are you sure the barrel is badly worn, or could it just be badly fouled.
A good dose of Wipeout would answer that question.

The medium length action CRF BSA's (sometimes referred to as the BSA Royal) are 7x57 length, so should handle the 284 case length ok.