I hope you get some ideas and may find this helpful. If you have other ideas please add them on.
I like the Imperial Guard vehicles. However the Russ needs help. The turret is way to small to load and fire the gun. So my solution is to use the existing turret and build a larger cover over it. Also I like to have removable sponsons. My solution is to add a side armor plate under which I hide magnets to hold the sponsons on. In addition the front weapon should be interchangeable and the barrel of the gun longer.

Here’s how I built it.
Russ turret with top and bottom plate. The bottom plate is cutout to rap around the existing russ turret with sprue piece to hold it in place.
The side armor has sprue added to thicken it to hold magnets.

Before the side armor is added I have a small piece of card to fill in the gap on the side

Then the side armor glues on. The small piece and the bottom holds the weight on the sponson along with the magnets.

See the barrel is cut and extended. The top and bottom plates are glued together on three sides.

I use this metal file to sand down the extra plastic. Works great but be careful as it cut plastic very easily.

Once it is clipped and filed down, the next pieces are glued on.

Then I clip and file it down to give me a nice smooth turret. Also no the front weapon mount for the bolter or lascannon. I cut the lascannon off and plasticard over it and then drill hole for a magnet. So either spare sponson bolter or heavy weapon sprue lascannon can attach to the Russ.
Now I can detail it any way I want.

