The short answer is NO. They won't even remotely fit. They used the No5 flash eliminator because they were already in production and available and the size of the crosspiece would ensure that with even the most worn out barrel and rubbish old ammunition, bullets would clear the crosspiece.

But you're sort of right in a way because the earliest EMER SA&MG V whatever it was, actually stated that the No7 bayonet WOULD fit a NO5 rifle and so far as I recallect, it was never amended. But it was a VERY expensive bayonet to make and notorious to keep in a serviceable condition