Variable Cam gear is about $100 on its own from anywhere like autobarn etc, not sure on how much Mock charge for it.
Is it possible that when the chain was put on, it was placed a tooth out, in the retarded position?
If this is the case, you could easily fix it by loosening the tensioner, and carefully moving the chain over a tooth. If it sits a little advanced it should still be ok. You can always give the dizzy a lil turn to compensate a little.
If it were my car, that's what I would try anyhow.
I have had my head decked on the EA, and chain still sits fine. I put in new chain guides, and was going to put in a new chain, but the chain was still in good condition, so there was no point.
Anyhow, God Luck.
CAUTION: Slippery When BOOSTING!