sorry about the poor image quality cell phone camera but here we go
pic one is the pieces you need two is the pieces cut at the right spots you'll need the middle of the grenade launcher and the top of the vox pic three is them lined up right. and the thing on the left of pic four is the finished hvy bolter. sorry I did not take a shor of it on the tank and they are unpainted the thing on the right is ehat it looks like if you leave the vox whole and clue it to the base of a trimmed extra coms from a chimera. also used half of the round part of a loader from the launcher to make my reloading chamber. though you can not really see it well in this shot. I use this variant for my bassy. there are the photos hope they help
BTW I know the pics are a bit crude but I promis if you look hard you can follow them as a diagram and with the above instructions make your own. and see your new near perfect hvy bltr whenever you want