That is odd. With the EPR, a low pressure cutout won't protect against evaporator freeze. It will shut down the system if you lose most or all of the charge, but that's all.
I will have to go back and watch the relevant Chrysler Master Tech videos. They talk about which vehicles used the EPR and which used cycling, but I don't recall if they mention what pressure and/or temp controls each system also had.
Did you delete the EPR valve on your 68 in order to run R-134a?