Hi BwanaBob,
I picked up a GEW98K in 303-270 a few months ago. Also really cheap, with a left hand stock. My thoughts were to rebarrel to one of the magnums. Years ago I scored a 303-25 on a VZ24 action and rebuilt to 358Norma Magnum. A mate of mine has one built on an M17, yes an M17 rather than a P14.
As far as the 303-270 is concerned I used a 303FL die to size some once fired 303 cases and then a super simplex 270 neck die (as I had one) then super simplex seating die. This process worked fine and then just neck sized when reloading again. Simplex still sell 303-270 dies in their Master series, but if yours is an improved chamber you may have to get a set of dies made. Would probably cost more than the rifle, although if you fireformed standard cases and then neck sized after that you could probably just dump them if they became too tight to chamber and start again. Simplex themselves could probably give you a fair bit of information on the early Australian cases. Here is a link http://www.simplexreloading.com/
Good luck with your bit of aussie shooting history.
LesLeeSpeed