This is what they look like, a long heavy zoom. Make sure it is f3.5 with a 62mm filter size. I've seen them with m42 and Minolta mounts, both with Focal brand, and one other as a Hanimex brand.

Just peel off the larger textured rubber strip to expose three screws. Remove them and unscrew the front element. Unscrew the lens, clean up the grease, and paint the inside of the shield black. You'll need a reversing ring and step-up ring to match your camera. I always keep a 55mm uv filter on the camera so a 55-62 step-up ring and a 62mm coupling ring do the trick.

When finished you'll have a nice, achromatic macro lens that is big enough to let you zoom in and out without vignetting over a large range.