The engine idles ok at the higher advance rate because it takes a while for the lean idle mixture to burn.

Do you have an amplified ignition box
Something along the lines of an MSD6al?
And are you using a dial-back timing light?
Perhaps one of the Penske ones from Sears?

I found when timing my 462" Buick engine (455 series engine) with a Penske dial-back it was off about 20 degrees.
The original timing light - also a Penske - a non dial-back style showed the timing where it should have been.

I've discussed the dial-back timing lights being used with an MSD 6al box on another site (HAMB).
Most of the guys reported that their dial-back lights read the timing correctly and compare favorably with a non dial-back light.

The readings taken on my - owned for a short while, took it back - light was with the dial set at zero and getting the degrees off the degreed dampener.

A couple things you could do.
Take a reading with a standard timing light and see how it compares to the dial-back light if in fact that's what you're using.

The other, time the engine statically at your desired initial advance figure.

The manuals show centrifugal timing starting as low as 430 rpm in some cases so your 700 rpm idle probably has part of the centrifugal timing in.

Timing the engine statically would show you where you're at there.

As far as your cam timing goes, I'm not seeing a crank gear mark other than the yellow or black line in the pic.