I haven't checked it but I remember setting it at 12 BTDC. It starts up nice doesn't fight the starter etc. I remember it didn't like the 5 BTDC book spec setting.
I was setting timing about a year ago I could go back over it.
A couple of points/explanations.
I'm going to assume this is in a '70 Dart and that was the shop manual you got the initial from.
1. The spec in the book will work OK in combination with the exact distributor that was a '70 340 that year; and that carburetor set to the exact specs.
2. The rpm of that initial timing is critical, particulalry for the late 60s - early 70s Clean Air System (CAS) cars.
12* BTDC is a good starting point. It will be worth finding out at what rpm that 12* is measured at.
For example it's possible that the 12* was measured at 850 rpm, but the distributor begins advancing at 750 rpm.
WRT the Edelbrock 750, they have some known issues which sometimes to often cause linconsistancy but mostly in the high speed system. I'll find the threads where this has been discussed.