G&G blowback upper receivers

[Sierra1_1]

So i want to get a metal body to replace the plastic one on my G&G GR-15 raider blowback, but the fancy blowback is a real pain to find a compatible upper other than G&Gs own which are near impossible to find. I don't mind removing the blowback it's just if i do the charging handle and mock bolt will not function! Has anyone been able to file down a non blowback upper to fit the gearbox with the blowback or will I be able to just drop in a new charging handle and bolt to a non blowback upper and have it work fine once the blowback is removed. Or does anyone know of a upper receiver that can fit a G&G blowback without modification?