I just did my 60 day extension based on marriage in Sri Racha Immigration Office.
It was quiet, 4 people ahead of me in the queue.
All the usual documents.
However I want to warn people they required TM30 as proof of your residence in the province, and also a Kor Ror 2 form from a district office which some offices don't ask for (in addition to your Kor Ror 3 marriage certificate).
Good luck with your visa everyone