As you say the 1800's are quite rare, the 1.8 CVH superseded it in 1989 in the Sierra.

I think the head probably would fit physically but as to whether it would run is a different matter, the question is why would you want to? You may as well just swap to a complete 2 litre later on.

Also the 2 litres are quite common have you looked on the bay? If not your local scrappy more than likely has one as they were in most Fords of the time, Sierra, Granada and Transits etc.

IMO there is no major benefit between the 1.6 and 1.8

The injection head/block is named so as that is the one that was Nativity in the Sierra 2.0 EFI and I believe the head flows better than a carb equivalent.

Martin