Right i want to buy a vr6 exhaust off my mate its had a decat pipe welded to a straight through power flow system and my car is a 8v gti

ive used the search option already i just want a few answers as not much about it on there!
1.firstly will the bolt holes on my standard gti downpipe line up with the vr6 system?
2.secondly will the bore sizes match up as its a aftermarket de cat i guess you will need to know the size well i dont know so think averages
3. i already have a decat on my standard 8v system but the rest of the cat back system is rubbish anyway the bore on mine is 2 3/4 inch which im guessing is about the same as vr6 anyhow?
4. using the search option on here i have read about buying adaptors from various places wheres the best place if needed?