Hindi siya kasya brod.
Yung cyma cm 048 kasi is similar to inokatsu/ guarder wherein the hop chamber is attached to the outer barrel that goes all the way through the rear sight trunion.
on the other hand, the hop chamber of kalash is similar to vfc wherein it is attached to a sliding piece of plastic held in place by another L-shaped plastic.
based on what you have said, it appears that you plan to replace the receiver of your cm048 but retain your other parts which is basically evertything else.
if that is the case, mahihirapan ka kasi hindi papasok yung outer barrel ng cyma cm 048 mo sa receiver ng kalash.
ang outer barell ng cyma mahaba at sa dulo nya, yung pinapasok sa receiver, parang "tuning fork", may dalawang bakal na nakalawit na kabitan ng hop. pag pinapasok siya sa receiver, tagusan siya. On the other hand, yung outer barrel ng kalash parang real steel, walang nakalawit na bakal and hindi siya tumatagos sa rear sight trunion.
thus, bilog lang yung pinapasukan sa receiver ng kalash while yung sa cyma cm48 hindi siya bilog lang, para siyang may 2 gatla sa magkabilang gilid para makapasok yung kabitan ng hop.
anyway if your problem is just the loose screw on the rear receiver trunion, pwede mo naman siya maayos just by replacing the screw with a bigger one. ni hindi ka lalagpas sa bente pesos sa ganung mod.