Remember, the shell holder on a MEC 600 type machine is a stamped piece of metal and has lips underneath to hold it down to the press's base. If using the same shell holder in a short kit you'll need to grind/cut these little lips off. Don't worry, this is what MEC does. The heavy center column spring will keep it perfectly aligned.

When an old man dies a library burns to the ground. (Old African proverb)