What is the correct (initial) timing for a 009 on a 71 (1600)?

A parts house told me to time it the same as the stock distributor, which in
my case equated to 5 degrees ATDC -- not a good choice I soon found out.
 Acceleration ceased, for one thing.

Since realizing that setting couldn't possibly work, I've gone to 10 degrees
BTDC, which is palatable.  But what is the 'spec'?

Anyone know?

Thanks in advance...