My choices:

1. A DR suitable for general plains game hunting, preferably also able to take reasonable long shots - a QD mounted scoped double in something like .300 Super, .300 Win Mag or 8x75R;

2. A general dangerous game DR preferably also able to double as a medium game rifle if needed - also scoped with QD mounts - in the neighbourhood of a .400 or .500/.416;

3. A big bore for following up dangerous game - .500 3" NE - express sights only.

Add a set of shotgun barrels to one of the above.