Hello Der Ami,
I actually had my son-in-law (a master machinist) modify my little RCBS "O" press once before. He opened up the 7/8" thread, to 1" when I got the big 577-500 dies. It only took him 15 minutes. He will do the same this time, opening it to 1-1/4" and then also making a 1" bushing to allow the 1" dies to be used also. This press is dedicated to my "Big" dies.
For regular loading, I actually have 7 other presses; 2 Bonanzas, a Dillion, a Hornady, 2 Corbins, and a no-name monster press dedicated to swaging.