Sinnis/Pulse/Superbyke upgrades

Hi all I need some advice on my Sinnis Apache.
I have started to upgrade the bike from standard and will write what I've currently changed if anyone else needs specs/info.
I've changed,
- Standard bars to Renthal (gold) £34
- exhaust to Toro race pipe (full system) £199.99
- USD forks (gold) £199.00
- LED headlight £7.99 each x2
- sprocket front and rear standard is 15 f 51 r new 16 f 48 r £35 set
- DID chain £35
- Michelin pilot tyres front & rear £120 for set
- handguards £45
- main jet standard 97.5 to a 102.5 come with exhaust
- oil filter to a hilow filter £4.99
- K&N fuel filter £14.99
Now my question is I want to replace air box I know the carb air inlet size is 43mm so would need a filter that size but what size do I need for the breather pipe or could I block it off instead?
Any help on air filter would be amazing