I don't know. Downsizsing 3cals extended shoulder length, likely beyond contact with the die. That is, shoulder area near the new neck-shoulder junction would not be under die control. This much will expand with both firing and body sizing, and then how will you bump it back?
Might work, might not.
I've been using a 270 Win full length die for my 25/06 to sub for a body die. Everything seem ok, but seems is a big word. Do you think this is a good idea. I'm not sure if all the shoulder angles are ok.