Visa for Ireland Passport holder

Greetings. I live in South Africa but I hold a passport from Ireland. I intend to cycle through South-East Asia next year. I intend to enter Vietnam from Cambodia at Moc Bai at the end of June 2017 and to cycle the length of Vietnam and exit 55 days later at the Chinese border through Dong Dang. Is it possible to apply for a 60 day visa and what do I need to do so? If not can I get an extension whilst in Vietnam? Kind Regards