Engine mounts on the body will be the same whether 1.6 or 1.8, but the mounts on the box itself would be different IF you switched to a PG1.
As per the otehr comment - you would also need to use your 1.6 flywheel and clutch if using the R65... Which does spring up another possible issue if you ran the 1.8VVC ECU (which I'm presuming you wouldn't?)
Anyhow - I'd recommend for ease:
1.8K
R65 box
1.6 clutch and flywheel
1.6 head (ported and flowed - even better with big valves!)
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