Making a custom siege engine....Liquid Fire Upgrade adapt?

I'm making the flame spewing thingy from the Outlands setting into a siege engine for a daemonic race...making projectile damage etc is easy, the general premise is its also the main ranged attacker, and since it throws fire, Liquid Fire would be the best upgrade...what things do I have to line up to make the upgrade transfer properly?

blarg...

Ok, new problem....fixed that easily, but how can I combine the liquid fire upgrade and the flaming crush thingy the orc demolisher gets...i forget the name...but is it possible to have them both on the same unit?