I bit the bullet and forked out for a Laylax medium length barrel for my Type 89 AEG. This barrel knocks about 70mm off the standard barrel length to give you a carbine sized gun.
This is all part of my '89 upgrade program and will hopefully result in quite a unique and cool looking AEG. I know shortening the barrel is something of a retrograde, but I will off-set this by installing a tight inner barrel at the same time.
The barrel was sourced from Fire Support UK at £50 plus shipping.