Probably just wanna send that mission to me for checking. I doubt that it's anything special so I'll dispose of it carefully for you.

Look at the location dogs on the gears. If they're machined undercut then it's an F3 box. If they're cheesy, rounded off non undercut dogs then it's nothing flash.

Or you could count the teeth and work it all out so that you know tha ratios, speeds at various rpm etc etc and then can cross reference to various model NSRs to see the difference. You can also amaze people telling them all about it.

That's what I'd do.