[Dead Parrot]

Original HEI or points? If points, did you remove the resistor wire/block from the power wire to the HEI?

Volt reading with headlights on, blower on max and wipers running while revved up a bit? (quick and dirty alt check while on vehicle). A downside to one wire setups is no allowance for voltage drop in main output wire under high load.

Double check for vacuum leaks.

Accel pump on carb working?

I run manifold vac for the advance but like others have said, try both.

With vac advance pot disconnected, a good start timing is around 8. Once you have your problem fixed, add more until it either gets hard to start hot or you pick up some pinging on load. This gives some allowance in case your timing mark is off a bit from true TDC. (It happens) Mine likes around 12 by my simple timing light.