I like upcycling/modifying these toys. Usually a fairly simple makeover, a few cosmetic additions like rivets and valves followed by a paint job.
This is the starting point
After sanding the whole thing I added rivets a fake zooming eye piece and valve handles on the side tubes.
Next I sprayed it with acrylic primer followed when dry by a spray coat of matt black acrylic paint. I finished it with a light coat of gold paint and a couple of coats of clear lacquer for protection.
This is the finished result.