Hey, just received my from ehobby a few days ago. you're gonna have to chop off the stock tube guide so that there's around 21mm left sticking out from the receiver. very easy. few minutes with a hacksaw.
But have to say i was a bit disappointed with the part. the tube is WAY longer than the one that comes with the complete APS aeg. compare pictures of the two closely before you buy if you're trying to go for the same compact ar pistol look. count the segments on the tubes and you'll see what i'm talking about.
the kit tube is actually 220mm long! longer than the actual receiver and weighs 456.5 grams w/o sling mount that is included with the kit. waay too long and heavy for what i was trying to build. its all metal with a nice finish.
looks hella fugly if you're planning to use with a short front set.