m4 ris and metal body

[MilataryMupet]

ok bassically i have decided to upgrade my m4 instead of bying a new gun as far as internally im gonna leave as its not broken so im not gonna try and fix.
ok its a G&G GR16 m4 and i want to put a ris rail on it and i am looking at a G&P m4cqb ris kit (long) i was wondering how i would go about fitting it if i got it i have looked every for a video on how to fit an ris system but i cant find one im guessing i will have to take the whole outer barrel of but i dont know how and would i need to change my delta ring?
also i broke my platac body and i want a metal one but as my gun has the wierd panamic blow back system i was wondering if any m4 metal body would fit or would i have to get a specific one

if any one could spread some light on my issue i would apiciate it
cheers
Greg