Yes, thats it. The 458wm was designed to duplicate the performance of the .450#2 but at much higher pressure.

But seriously, it can be a good conversion, the big rim will give better extraction bite than the WM and in the super strong No.1 action, if you want to hotrod the cartridge then I can't imagine what you could get.
Its a great cartridge for the range, "what the hell is that" factor and the simple act of sliding a pair of 4 1/2 inch cartridges into the breach makes me smile.

The Lott uses nearly 3 times the pressure to get only 100 fps above double rifle 450#2 balistics. In a no.1 you can duplicate them as there is so much spare powder space. A square shows 465 grain solid 2210 fps at only 26,000 CUP the same velocity in the Lott is 50,000psi. Or use something like trail boss or 5744 to get 45-70 type performance for NA game.

In the .450 Assegai A square are getting 2400 with a 500 grain at around 46,500 psi. The case and the 450#2 appear to have around the same capacity although I am just working on the dimensions and don't have a water capacity for the Assegai.

Good luck with whatever you decide on, love the No.1