Update
Thank you so much to all who responded
Spent three hours trudging up and down Lamington road, to no avail
Almost all dealers recognised the tweeter immediately as a OEM Bolton, all of them said that even an equivalent won't be available.
All of them said more or less the same thing, replace one with a modern one. If I like it then replace the other three.
None could tell me the ohms nor Watts. They did say that if I can get old stock of Phillips, Apex or Bolton of the same diameter plate, then it will be the same.
A repair tech said that if I get a paper cone tweeter of the same vintage, even with a small difference in size, it will be the same
By various conversations with all the people today, I've come to the conclusion that in the 80s technical parameters were not considered. You just bought a 4 inch paper tweeter to replace a 4 inch paper tweeter
Buying a modern tweeter to replace is to go by ear and keep the tweeter that you like. In my case buy one to add, if I like it keep it, if I really like it then replace the other three!!!
My last attempt will be to send my sample to my tech, who also said the same thing to me today, he will find a 4 inch tweeter for me!!!