Any rifle you can shoot well out to 300 yards will probably work for you, as long as it shoots a bullet bigger than .22. and heavier than, what, 100 grains? I see no reason why your 8mm won't work for you. It will just have more drop at long range than some of the faster bullets with better ballistic coefficient. You'd need to know your drop at various distances to make it work.
Your Dad's recommendations are good. My personal preference might be the .260Rem or 6.5X55. But that's just me.
I am Pro-Rights (on gun issues).