The nose cone probably encloses the gunsight radar ranging.
The circular object in the intake is associated with (ie it's a housing rather than the gun muzzle per se.) the 30mm ADEN cannon - one each side. I think it was 60 rounds per gun. I hate to think what firing did to disrupt the intake airflow, but if there was a problem I guess it was made to work a la Hunter and Swift (not.)
Apparently it is difficult to distinguish between the Folland or HAL-built Gnat F.1 and the HAL-built improved Gnat that they called the Ajeet. It could be either.
Scuttlebutt says the Yanks wanted 500 but when Folland heard they were to be used as targets they threw a wobbly and declined the order