For example guys, if i had mk2 8v GTI (digifant), or i got mk3 8v GTi (simos) could i use 16v kr/pl/9a/6a/abf head easliy on mi 8v GTi ? or i got mk3 8v GTi (simos)

What else should i change apart from heads.??

thanks...

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POLO 1.6 8v '98
POLO 1.4 16v '98