Brass Ensign carbs on the Cat Ten and Fifteen

A nice collector here in Oz had a Cat Fifteen with a brass Ensign carb and he suggested to me that the early Cat Ten and Fifteen tractors were all fitted with brass Ensign carbs, and later one's were fitted with the pot metal Ensign carb, but when I asked a couple of highly respected guys I know, I got told it wasn't that simple.

One guy I talked to suggested there never were brass carbs on those tractors, and if you have one, it came off a 2 cylinder starting motor for a diesel Cat, you can tell straight away because the throttle linkage is on the wrong side. Another gentleman suggested the brass carbs on the Cat Ten or Fifteen got removed during WW2 due to the shortage of brass, and replaced with the pot metal carb, so I'm more confused than ever.

It's a shame Bill Campbell passed away because he was the Ensign carb guru, I contacted him years ago and he had carbs available in both brass and pot metal for the Ten and Fifteen, but can anyone clarify exactly what the situation was with brass versus pot metal Ensign Bet and BeV carbs, because I need 5 carbs for my old wrecks and I'd much rather have brass than muck metal if new one's were being made.
Thanks 

https://www.thecarburetorshop.com/TrackitsC.htm#TracCate

i have had both brass is much better hard to find. both of my 15s have brass. i know the early 15s came with brass because my pv 536 has always been in the family.

The guy here in Oz said the 15 he owned came from the original buyers family, so he knew the full history of the tractor, and it had a brass carb on it from new. Byron Heal in England told me they are not actually brass, but Naval bronze.