I haven't seen a McCulloch 25cc, so I' not sure. They could be very similar or even identical. My understanding is that Zenoah OEMs these for many different brand names, including Echo, Cub Cadet, Troy Bilt and even the Pro-grade Ryobi 2079r. They are equipped a little differently from brand to brand. My Cub Cadet 25cc shown below comes with a Walbro WYL fixed-jet carb and single piston ring. The Echo shown above, OTOH, is typically equipped with a Zama carb and dual piston rings.

I originally was gonna use the stock magneto ign, but the whole enchilada ended up weighing close to 4lbs RTF, thus negating the one major advantage of these engines - light weight. I've since had CH fit it with a timing kit, and I'm gonna try it with CH ignition, and also on glow.