To avoid a full synch of the bitcoinabc.org wallet can I point it at a copy of the core blockchain?
Surely. Maybe try:
- Close both Bitcoin ABC and Bitcoin Core.
- Locate the "blocks" directory for each implementation.
- Backup ABC's blocks directory.
- Copy the contents of Core's blocks directory to ABC's blocks directory
- Start Bitcoin ABC.
I'm not in a position to try this so I can't be more precise.
Given that Bitcoin ABC is a derivative of Bitcoin Core, I would expect it to be able to handle the situation. It will probably want to rescan or something but it shouldn't try to download the blockchain it already has.
If it fails then you can recover from the backup and continue syncing. You could also think about waiting for Bitcoin Unlimited's implementation.