The M-03M's new lightweight knuckles are a smaller than the standard suspension ones.. they don't make aluminum ones, and I doubt they will..

In order to use aluminum knuckles on the M-03M, you'd need a few parts..

4 x 5x11mm Bearings (standard Tamiya hub bearings)
53523 - Aluminum Uprights
50736 - B-Parts Tree (has the C-hubs for uprights)
53141 - Lightweight King Pins (ones included won't fit)

Some actually do this (mainly transplanted from their old mini) for practice, then switch to the lighter ones for racing.. but even then, you're only saving a few grams..
I'd take the durability up front with the aluminum, and leave the LW ones in the back since they're 2-degree toe-in.