I have not done it.
What you describe sounds like it will work,but you already knew that.
Necking up with standard reloading dies.in my experience,;There will be one side of the neck more prone to stretch.A softer or weaker side.This is where the stretch occurs,resulting in non-uniform neck wall thickness.This,in turn,makes for non-concentric ammo.
So,then,to fix that,a guy starys thinking about neck turning.
In my experience,the 416 Rem kicks pretty hard.Hard enough that its too much for me to enjoy shooting.I think you will need good neck tension to hold the bullets in the case.
I have had best luck necking up using the Bullseye/Cream of Wheat method.I get better neck uniformity.I have used it with 35 Whelen from 30-06 and blowing 30-40 Krag brass out straight for BPCR brass.
Once .405 Win brass and factory 35 Whelen came out,I do not require fireforming.If you need more on the Cream of Wheat method,ask.Use virgin brass.
Of course,best case,find new .416 Rem brass.
If a 416 is needed to shoot whatever you are shooting,I would not make any compromises in my ammo.
Next best might be to see if Huntington or someone offers magnum basic brass that you can neck down.