Andy,
I will turn my speaker on my lathe [and I would think Arno will too], but before I got that 17-21 used to be amazed at what I 'turned' using my Dremmel fixed in a vice!! This is what I did for my Arun class aerial reducers and cappings. So that might just be the one way forward......then start dropping hints for a lathe [birthday] my wife bought mine for my 60th birthday some thirteen years back!! Seriously, another little idea to get the 'funnel' could be to find a small plastic syringe [or similar] and cut off the conical reduction section and glue this to some styrene rod/tube [maybe a little fettling to get it up to your fine standards]. Then I think all those little fins on the back will just have to be cut out and glued into place using spacers......that is what I will do - when I get there in 2025!!
Cheers, I am sure you will come up with another 'little gem' - but here is a 'starter for 10'!!
I'm back to the workshop for a little while now, to take the excess solder off the supporting fins on the gob-eye fairlead bases that I did this afternoon.
Kim