m16 --> m4
 

i have a g&g m16 RIS, and im not particularly fond of the length. if i wanted to replace the frontend, what parts would i need to replace in order to convert it to an m4? i was thinking a shorter rail system, outer barrel and maybe buying a silencer-barrel extension provided it is the same length as my inner barrel? am i missing any parts?
(the stock is fine the way it is)

Maybe a shorter gas tube too.

I think you have everything covered.