It was a fairly easy conversion.
I started out with an L shaped piece of plasticard. This would be the seat.
Next, I took the SM sgt and removed his legs and arms. I glued him to the L.
I then created the Heavy Bolter using some regular plasticard and some thin round for the barrel. Just cut out so it looks like a normal HB. Make sure you add the ammo case and the ejector port. When making it, also incorporate the swivel mount into the gun itself. It needs to stand above the marines legs.
Sculpt the SM legs and feet with GS. Leave a slot between the legs for the HB.
Once dry, glue the HB in place.
From there, I created the SM's arms out of thin plasticard rod and his hands out of GS.
Finally, I used a piece of round sprue for the wheel and GS'd a fender on it.
I kept things more rounded because I wanted it to fit with the bikes style. If I had a new one, it would have been more squared.

