I don't have this IC so I have a question if LT4320 will work properly when it's powered from half of the rectified supply.
Nominal AC voltage is 42V ±30%.
See attached LTSpice file.
This circuit will not work. LT4320 relies on the OUTP pin sensing the output voltage for proper operation. Also, 42VAC with ±30% tolerance exceeds the recommended 72V peak operating voltage range and is close to the 80V absolute max for the IN1, IN2, and OUTP pins.