Hi Andy, yes I have a toe in the microwave camp too! The Racal block has a 'tweaker' available through the rear panel but I am not sure whether it is a pot or a cap yet. I have one of each here. Yep
When heating a xtal up for the first time is a good idea to burn it in . Leave the heater active for several days or longer and then you may find the frequency may have shifted but will stay where it