Running simple non return valves in the tubes which feed each side of the diaphram is all that is needed to control an advance/retard set up. If you have the springs changed so that the retardation only kicks in once a high boost level is acheived would be best. The smartest way to circumvent detonation is by the implementation of water/alcohol injection. There are numerous ways of acheiving this. And some of the cheaper ones can be the most effective, when set up properly. I have a c32 laurel washer bottle which can pump 13psi. Through a .040 oriface, it can pump nearly a litre a minute.
I've read untold anectdotes of suprising gains atained from this method.