I bought SA body with gearbox and cant fit chamber,its too long and magazine not fit and and dont know how seal chamber with gearbox because there are two groowes witch i never see on other gearboxes...
the nozzle length is just a case of getting a longer nozzle, there will be a correct size for your particular gat.
you don't need to seal the gearbox to the hop unit, the key seals are:
piston o-ring to piston rear face
piston o ring to cylinder
cylinder to cylinder head
cylinder head to nozzle
nozzle to bucking feedlips
bucking to barrel
so the 2 cutouts shouldn't be relevant, although one wonders how they bode for gearbox strength.
what i'm seeing here is a case of aftermarket parts not playing well together, the nozzle is a relatively simple case of being the wrong length but it sounds like the hop just don't fit the gun well.
welcome to the wonderful world of "compatible-ish", don't matter how good a part is if the gun don't like it.