One hole had a 6mm tread in it, used a copper washer and bolt to stop it leaking, that was on the left hand side.
The other hole is about 15mm used a plate and gasket to seal it, it's just behind alternater.
Don't know what they are , need schematic of the original car and block . Possible blocking them off and restricting the oil has caused pressure build up causing oil leaks ? Who knows , PCV valve fitting , sensor ......................?