What Jets? 670 Holley

15-16 initial and limit the distributor. It may require taking the distributor apart to do it. How much mechanical advance in the distributor? Make sure you are setting initial with the vacuum advance disconnected and plugged off. See the instructions. If you reconnect the vacuum advance and the timing jumps up to some huge number at idle, something is wrong

If that thing has a vacuum advance, make sure it's on ported, not manifold vacuum.

Don't mess with the jetting at all until you have the timing and curve straightened out.