You cannot tie the LCD's RS and E to +5V.

RS is the "Register Select", and it needs to select between Command and Data registers for the LCD to work.
E clocks in the data nibbles, without the clock the LCD never receives data. It is not just an "Enable" pin.

GPIO.3/MCLR/Vpp when not used as MCLR, is an Input Only pin. You cannot use it for the data bus output.

There just aren't enough pins on a 12F683 to drive an LCD directly.
You can do it with a shift register, or port expander. But if you are going to have two chips ... you might as well just use a bigger PIC to begin with.

Mike did a strange little circuit here that uses the serial data to control the RS bit. Which means you have to send two byes serially for every byte sent to the LCD, and you have to bit-bang the LCD routines since LCDOUT will not work.
But then again ... WHY? When you can just use a bigger PIC.