|Lasplas never looked so evil.|
Heres how I did my razorback conversion for Chaos.
I took one side of a lascannon from the sprue and one side of the heavy bolter and mixed them together.
The Heavy Bolter had the head of the gun removed and filed down along with the back,
A chaos knight shield was added on top and a peice of plasticard tubing was placed at the front of the Heavy bolter to represent some early pre heresy weapon which is the twin linked Plasma gun.
I attached them to the turret from the Ageis defense line for this one here but you can use the normal turret piece as well.
Hope this helps you guys as it was incredibly easy for me and I suck at modeling.