Thanks. @Wizcrafts I did buy all the narrow needle plates & feed dogs from @Patrick1 except for the #20 plate & feed dog.
I was hoping maybe I could just swap between the #23 & #25 plates & make a few minor adjustments to swap between 138 & 277 thread.
I've read about a few members saying they got their class 4 machines setup, where all they do is a needle & thread change to swap thread sizes.
I have been trying to find articles on here about adjustments from 1 thread to the next on the cobra class 4, but I havent had much luck.
Thanks for the link. I will take any advice given.