You even don´t need the LW suspension on the standard 415. I´m using the old suspension on my MSX and that is working very good.
Tamiya always said the MSX conversion is for the 415MS or 415 + LW suspension but that´s not true. Because of this I also was unsure before if the old suspension would fit the MSX but it´s good this works.
Classic RC - http://classicrc.wordpress.com/