Ahhh - you do realise that the two engines have significant differences and in fact belong to two different families - the 1.6 is the G series, and the 1.8 is a J series - the J series are quite a bit larger.
The 1.6 bore is 74.9mm (2.95in), the 1.8 bore is 83.9mm (3.31in) - so quite a bit larger and no, I don't think they'll fit.
It is possible to shoehorn a J series engine in, and if you want to go that route, consider a J20, they are physically the same size and there are more of them around.