Will the clutch fiber discs from a 74 DT175 work in a CT3?
74 #437-16321-00-00
73#132-16321-01-00
Or, does anyone have a spare part # Barnett YPK3?

Pretty sure thickness changed.

Thanks Mark. I was thinking that too, but wasn't sure.
EBC list a part number CK2209 according to tech support
but when I searched that number, it was showing for a 74
also. I am starting to wonder about trying the china ones
that are on ebay. Freaking discs from Yamaha are 27.00
each. Almost as bad as their pricing on points!

I'm not sure where you got your part numbers in your original post but just double checked and they went to 3mm in 1976. 

Earlier 175 are all the same 4mm thickness so same functionally except for maybe minor supercessions over the years.. 

Somewhere I read that there was a change, but couldn't find the info
again. I ordered some oe from a person on ebay, but have not received
them and can't get them to contact me. Will cancel them and give the
others a shot. Part numbers are from Speed and Sport web site. Thanks
for the response. D