I would set it by ear, and performance.
There are contributing factors, however, about 6 degrees advanced or BTDC., should work best.
NO. Not even close.
Approximately 5 degrees before top dead center if the motor isn't set up for high performance.
timing for the 454 engine is 10 degree's at TDC at 700 rpm in neutral or park
5 qts. with a new filter.
In the 1970 Chevrolet Impala, the 250 L6, the 350 V8, the 400 V8 (small block) and the 454 V8 (big block).
1970-71 Chevrolet Small Block 400cid heads.
There was a 396 available in all Chevy trucks from 1968 - 1970.
It is bolted to the engine block or oil pan.
on the back of the motor driverside cast on the block
is a V8 big block engine in a Chevy or ford in the 1960's to the 1970's
According to my Chilton's Auto Repair Manual : For a 1970 , 429 cubic inch V8 ( 5th digit of VIN is a " K ' or an " N " ) The ignition timing is 6 * BTDC