I would like to use a modified version of this circuit with the Vin gauge being 13 g and the Vout (load) being 14g in an AC circuit. Aside from changing the op amp,and R6 how can i make this suitable for an AC circuit?
It is not possible to use this type of circuit to limit a 20A AC line current unless it can dissipate hundreds of watts and withstand thousands of volts. (3kV)
In order to define a solution, you have a duty to define the problem with measurements and expected over-current limits and time duration.
Start surge current limiting is sometimes done with NTC poly-resitors.
It is always easier to limit current by regulating the load.