If you are not going to trim, only form, you may be able to set the die as needed and screw the lock ring on to the bottom.
I am not familiar with the Co-ax enough to say for certain.
Actually the lock ring isn't tightened to the press but only to the die body. The dies are allowed to free float so to speak in the slot allowing them to align better with the brass when sizing and seating. Best picture I could find.
I'm hoping the Redding Trim & Form die is as long as the die in the picture, at least to the top of the lock ring. If it is then it should work.