Really close!!
But I think I would try it like this.

Code:
ADVal VAR WORD
Quanta CON 342     ' 350 / 1023 * 1000
LCDVolts VAR WORD
Z   VAR WORD     'DUMMY VAR
Z1  VAR WORD     'DUMMY VAR

ADCIN 0,ADVal
	Z = ADVal * 342
        Z1 = DIV32 1000
	LCDVolts = Z1