For my '68 Impala with the 307, 4° BTDC at 600 RPM with the vacuum-advance line disconnected and plugged with a golf tee - but I could be wrong. That was a lot of years ago.
Good spark? The sparks should jump 1/2 inch to a grounded surface. If you have to hold the wire really close to get small yellow sparks, these will not fire the engine. That would be caused by the condenser or the coil, both of which are best checked by substitution. DC tests (ohms and volts) won't find an open condenser or shorted turns in the coil.