Advance springs

Can someone point me in right direction with respect to distributor advance springs

Stock 318 /stock converter 904/273 rear gear.. driver.

The stock springs are smoked and im getting some mechanical advance at idle causing the timing to jump around.

I prefer a smooth idle. Here is what I am working with.. one soft and one heavy spring. See pics.. heavy is stretched out.

I idle about 700-750..

Looking for a starting point on what springs and where to buy.

Ive searched and the choices are exhausting. Just looking for recommendations on what works for mostly stock setup. Maybe a little hotter than stock

Thanks.