If you want a lever gun (an excellent choice) and for some reason don't want 45-70 (which will stop a bus at 150 yards) then here's another thought: the Winchester Model 71 in .348 WCF. These are current catalogue, but not sure if available in Oz.
For comparison:
.358 WCF (better than .35 Rem…)
180 gr (12 g) SP 2,700 ft/s (820 m/s) 2,914 ft•lbf (3,951 J)
200 gr (13 g) SP 2,500 ft/s (760 m/s) 2,776 ft•lbf (3,764 J)
250 gr (16 g) SP 2,200 ft/s (670 m/s) 2,687 ft•lbf (3,643 J)
.375 WCF (the modern big brother of 38-55)
200 gr (13 g) JFP 2,223 ft/s (678 m/s) 2,194.12 ft•lbf (2,974.83 J)
200 gr (13 g) JFP 2,419 ft/s (737 m/s) 2,598.09 ft•lbf (3,522.54 J)
220 gr (14 g) JFP 2,029 ft/s (618 m/s) 2,010.66 ft•lbf (2,726.09 J)
220 gr (14 g) JFP 2,236 ft/s (682 m/s) 2,441.85 ft•lbf (3,310.70 J)
.348 WCF (one of the most powerful rimmed cartridges ever in a lever gun)
150 gr (10 g) 2,890 ft/s (880 m/s) 2,780 ft•lbf (3,770 J)
200 gr (13 g) 2,530 ft/s (770 m/s) 2,840 ft•lbf (3,850 J)
250 gr (16 g) 2,350 ft/s (720 m/s) 3,060 ft•lbf (4,150 J)
.375 H&H (The minimum requirement for elephant hunting in several countries)
200 gr (13 g) JFP 3,195 ft/s (974 m/s) 4,534 ft•lbf (6,147 J)
235 gr (15 g) SP 2,964 ft/s (903 m/s) 4,585 ft•lbf (6,216 J)
250 gr (16 g) SP 2,835 ft/s (864 m/s) 4,463 ft•lbf (6,051 J)
270 gr (17 g) FS 2,694 ft/s (821 m/s) 4,352 ft•lbf (5,901 J)
300 gr (19 g) SPBT 2,645 ft/s (806 m/s) 4,661 ft•lbf (6,319 J)
And, a stout 45-70 lever gun load (Marlin Guide Gun)
300 gr JHP 2,275 ft/s (693 m/s) 3,449 ft·lbf (4,676 J)
The .375 H&H is a serious big game round and the minimum for elephant in several African jurisdictions. It will take down a camel. It will take several donkeys end to end. It just seems a little much. Furthermore, rifles chambered in .375 H&H (there are no lever guns so chambered) tend to be somewhat pricier than other options and will be only bolt action, singles, or double rifles.
If the Winchester Model 71 in .348 WCF is available there, it would be my second choice, after the round that just about exterminated the North American bison, the 45-70, available in several Win and Marlin options and, for those who like more risk, the Rossi.
For an interesting read on the 45-70, the results of the Sandy Hook Trials 1879 (not to be confused with more recent and tragic events) may be edifying. Big and slow makes big giant holes.
http://www.researchpress.co.uk/longrange/sandyhook.htm