First, you need to make a intro post so we can see your history in airsoft.
Well unfortunately, I am in the same boat as you. The base of the gun is a type 96, so any aps2 type 96 parts will do. There was a website that had a really good page but I cant find it.
First I wouldn't worry about the outer barrel, second its not going to be cheep, be prepared to spend around 1000 in upgrades.
http://www.airsoftatlanta.com/Airsoft_Type_96_APS2_L96_s/279.htm
This link is the only place in the US that has type 96 parts, the hop-up you need to change to a PDI(
http://www.airsoftatlanta.com/product_p/66229.htm out of stock) to accept AEG cut barrels, the stock hop-up will break after awhile. When you get the new hop-up you can get what ever length you want, as long as it is a AEG cut and you have the PDI hop-up for AEG CUT. To add a silencer you need this
http://www.airsoftatlanta.com/product_p/25903.htm also a CW I will say it again Clock Wise silencer for this adapter, unless you get the adapter but it looks ugly. The stock barrel length is 495mm( with a PDI hou-up) I would not go any longer then 600mm for the reason that the gun would be too long and unwieldy. I am sure fuzzy or any of the others will agree that it is not a cheep process to get a truly beasty( I don't think that is a word) gun.