Eddy 1407

Isolate the intake tract. Disconnect and plug anything and everything that is attached and pulling vacuum, dist vacuum can, PCV, PB, everything. Sounds like it could be a huge vacuum leak. Check carb linkage for interference with intake manifold.

Don't know the cam, says it has 15*timing at idle but that may include some mechanical so when RPM drops, timing drops out and the issue escalates.

my 2 cents, start the car, set timing at 1K rpm to 25* and try turning the idle speed down. See how it responds and if you still have 25* as the idle drops.