Today I got a look inside an AVL crank case that has the breather lump on the left side like the Iron Barrel .
It has the old school recess in place just like the Iron Barrel.
If yours has the lump then in theory you should be able to to do the old school duck bill reversion mod.
Br. Blltrdr has pioneered and tested a method of making the mod with the motor in place to Iron Barrels that have said lump but weren't drilled for the earlier breather system.
http://www.enfieldmotorcycles.com/forum/index.php/topic,5572.15.html It should work even easier with an AVL as there is no distributor to get in the way.
The lump disappeared from production in the '07 time frame I think.