Wouldn’t the main difference be that instead of interal CM’s you’d have to carry the BOY pod instead of the spare fuel tank?
Again still waiting on all Viggens to get the BOY pod gaijin…
I don’t know exactly how they would look like, all I know is that there is the initial JA 37 and that small upgrade packages got added to the entire fleet over time without any change in designation. Then the JA 37D got made and all the aircraft which didn’t get upgraded to D standard were named JA 37C. Internal CMs were present before they were split into C and D since the C has them in the first place even though nothing changed for them other than that they recieved the C designation to distinguish them from the D, the initial JA 37 didn’t have them but how early the internal CMs were tacked on I have no idea though.