There's decent load data in Graeme Wright's Shooting the British Double Rifle, which you ought to be able to get ok as it was published in Oz.

Don't let this put you off but John Taylor in "African Rifles and Cartridges" said:-

"BSA used to build a Lee actioned magazine rifler to handle this shell; not a very powerful one, as evidenced by the fact that the Lee action could stand it. It was not suitable for general African use, as it lacked power and penetration I only heard of one man who appeared to be satisfied with it - he must have been easily pleased!"

But do remember LSA made rifles are quite rare as Lee-Enfields go