There is no specific size of the mirror. Only suitable mirror available in the market for this purpose is Old Lancer Box mirrors. You can find it in Panchikawatta under Rs. 2500.
As I know there is no specified length of bonnet either. But the examiner ask the model of the vehicle before they recommend the licence under monocular category. So, the vehicle should have a sufficient bonnet length to fit the mirrors. When you sit on the driving seat, you should be able to see the objects through bonnet mirrors up to some extent. (these bonnet mirrors do not provide clear vision scope than the usual side mirrors)
After fitting bonnet mirrors, you'll have to show it to examiner of RMV (either RMV head office or district office), and they will examine the vehicle. (apart from bonnet mirrors, they will check engine number and chassis number of the vehicle).
Inspection report of examiner, medical report, vehicle CR and other relevant documents will be scanned to RMV system.
No disable badge or sticker pasted on the vehicle and no additional conditions are mentioned in vehicle CR. So, don't worry for that. No one would know you have a monocular driving license, except for people who are aware of the story of additional mirrors.