GRX Ultrega compatibility

I have an old Ultrega 6800 LHS crank arm with a 4iiii power meter fitted, does anyone know if it will fit a GRX crankset as a direct replacement for the GRX LHS crank. And will the pedal be in the same position or will it be more inbound or more likely more outbound ( I think the RHS side is 2.5mm more outbound ) Thanks

There’s a couple of mm Q factor difference between GRX and the road arms.  The left pedal would be closer to the bb than the right,  A couple of 1mm pedal washers could take up the difference and still be safe?

Thanks, hadn’t thought about pedal washers