Oh, so there are no 1.8 block that's plug and play with the 2.0 16v 😑Nope, you get it wrong.
1.4, 1.6 eco block is M659 14 - approx 230 mm height
1.6 cf2, 1.8 cf3 block is М654 15 - approx 250 mm height
1.8 cf3 is М646 17 - approx 265 mm height
2.0 cf2, 2.0 cf3 is M647 19 - approx 290 mm height
Check this table for reference - Alfa Romeo 16V Twin Spark
Would have to use shorter rods or shorter pistons to make for the 265mm Vs 290mm difference in block height.
But by the way when you state engine block height, are you stating block deck height (measured from the crankshaft till the upper part of the engine block?