I built up a 25 35 Ack Improved years back. As I recall, if I went straight into the 25 die with new 30 30 brass, I lost way too many cases from crunching the necks.
Only way I cured it was to go into a 7 die first. Cant recall which 7 I used, likely a 7 57 die. Of course ya have to dink with adjusting everything, and just hit the neck only, THEN go into your 25 on the next step. I dont see why any 7 die with the short enough body would not work. 7 08 etc.
Of course that the case turned into an improved, has nothing to do with the process of initial necking down. Same process would work with your conversion. Not enough brass is being moved to worry about needing turned, Just check overall length I guess, though I doubt they would grow TOO much when dragging the expander out, and a little lube inside cant hurt either.
Typically separation comes from being resized too much, even with a light load. Neck size only, and brass will last a long time with light loads. Of course ya might not be able to interchange brass with different guns.