For the exhaust: Supersprint Australia ? performance exhaust systems. Be aware that due to age, Supersprint aren't producing products for many Mk4s, you'll have to check if the R32 is included (unfortunately the Bora V6 4Motion is ).
Regarding port & polish, that might be harder. We got so few VR6 engines here comparitively that there's very few people in Australia with good experience on them in this sense. There's a company in the UK who have quite a lot of experience, they'll do port&polish work on a head-swap basis, though you're up for quite a bit of shipping...
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