I changed from a 1.4 to a 1.8 mate (used the 1.8 as It was low miles and cheap) but bought It as a complete car It really Isnt that difficult then If your handy with the spanners I have upgraded suspension for the extra weight as already mentioned...

Basically change the engine loom and ecu (so u'll need the chip from the key for ecu)
change over your mechanicals (I used st exhaust etc so binned std 1)
The wiring going back to the fuel pump had an extra black wire which I didnt need so cut that as when It was connected car fired but wouldnt run(or use different fuel pump/tank which matches your wiring)
Fuel lines etc dont need swapping over mine are still 1.4 anyway (extra vac pipes from Inlet manifold I blanked off)
I havent had any problems cars been fine..

If your cars done how you like It go for It