You can turn the rims down on a BR case to fit in a drop port, but I don't know if the nose of the drop-port bolt would hit the case body, which of course, you can't turn down. And I believe the "drop hole" is larger for the drop port BR action.
I think a faster twist barrel & sticking with the PPC will work fine. Both Ray and Roger Haney had a thread on the PPC for 600 yards a while back, and Roger had a fast twist barrel & was getting close to 3,000 with a 105 Berger (or something in that weight range). Roger isn't afraid to tip the powder jug, of course. Believe he was using 748, but you could check the archives.