I decided it would be prudent to draw the cases out as close to cylindrical as I can and then resize them back.
That worked quite well although it took four steps per case with a silly variety of dies and expanders.
I was very fortunate to source some of the Hornady 270gr RN bullets on GunBroker and from fellow N.E. member 3DogMike so will be right with those.
In my GB purchase I also received a box of cast 265gr gas checked and lubed bullets which I think could be helpful in fire forming the brass before full power loads are made.
I have seen reduced cast loads with IMR4198 (which I have a bit).
Would it be appropriate to load these with the bullet touching the lands with a nice firm bolt closure insuring the rim is up against the bolt face?