Every symptom you have except the firm front brakes indicates air in the lines. Proportioning valve noise says its one half of the valve tan the other, the noise is it trying to compensate. The idle surge is probably the same thing, the diaphram is extending further than normal trying to compensate, pulling more air out of the manifold, computer senses mixture leaning and compensates giving idle surge..
My bet is you still have an air pocket somewhere. Im pretty confident Im correct.
Not to sound arrogant but are you sure sure that every thing is tightened and not leaking?? This could also cause the problem...
Its just an annoying bubble. Try getting more aggressive in your bleed. Back flush it if you have to, or power bleed it..