Just my two bits worth-
I might have said this before, but, my whole bike is predominantly made of bits that others would have 'binned'; far-que that-!...there's busted and bent fins from the alloy head, and it runs fine....
For what it's worth, the way I see it, I built it to ride, and it's no show piece, but constantly have all kind of folks pointing and giving thumbs up and asking 'wow what is it' (motorbike idiot..!..nah jokin') and sometimes even young guys saying their Dad had a BSA blahblah (there's no badging-for now)
Bottom line is, fix it next time you have a chance if you really need to, and if anyone points out you have a broken fin,
end the conversation