Psg-1 metal body/ PDI chamber question

[W0lf]

I've picked up a psg-1 and bought the above parts, but upon reading the vague pictures on the pdi chamber box, it wants me to cut off the two front tabs from the reciever. Now these things are super hard to get hold of and cost £120, so I thought I'd ask the question before I take a Dremel to it lol. Anyone fitted one before?