The 1.6 and 1.8 cranks were the same.
Not according to the part numbers. The different part numbers indicate that there is
A 1.4 block won't be able to take 1.6/1.8 liners without boring out.
This is incorrect. The blocks are identical (same part number for all sizes of the damp liner engines). The external measurements of the liners are the same for all capacities of 1995 on damp liner sizes.
Also the 1.8 blocks tended to be casted better and were thus considered "stronger" but that is essentially irrelevant due to needing a 1.8 and also poorly sourced as different eras brought about better 1.4 blocks so not worth worrying about anyway.
No idea where you get this information from, but we have never heard of blocks being cast differently for different engine sizes before. It does sound suspiciously like the sort of stuff that gets peddled on facebook - I usually regard anything posted on facebook as being rubbish (on further research, it very often does turn out to be completely wrong).
The only time I recall anything being mentioned (when MGR was still in business) regarding castings being selected for casting quality and liner tolerances was related to 1.8 engines destined for Land Rover. The only significant changes to the block design and method of manufacture came with the Chinese manufactured versions (Nanjing 'N' series, and SAIC Kavachi TCI Tech).
To put it simply, if all
that is required is the block casting, any version of damp liner K series will be the same.
If however, you want the correct liners, one from a 1.6 or 1.8 will do, but if you want a 1.8 crankshaft, you need
a 1.8. If you need the correct con rods, and pistons, you need one from a 1.8 VVC only (and some of the earlier 160 VVC engines had the same con rods and piston crowns as the previous 143ps 1.8 VVC, whilst further into production, the con rods for the VVC were strengthened and the piston crowns altered slightly - these latter piston crowns had '160' stamped into the casting).