Well this is my version of creating a Lascannon with Twin-linked Plasma Gun.
It did not take very long and all you require is
2 Plasma Guns
Green Stuff or filler
First thing to do is trim off one of the lascannon barrels at the joint where it will leave you a nice flat surface to glue the plasma guns on.
Easy peasy, then all you have to do is wait for it to dry and paint away.
Any questions then please don't hesitate to ask.