The differences between the two types (large transports and small normal catagory rotorcraft) is night and day, and NOT in the small helo's favor:
Part 29 requires fire zone integrity that is massive, so that the fire zone withstands the fire almost like a home oil burner firebox, for at least 15 minutes. Also, the fire detectors and extinguishers are all required as part of the design.
Part 27 has none of this at all, so that a fire can rapidly spin out of control in a "normal" helo that a transport can withstand with impunity. However, most recips have no fuel pressurization in the fire zone, so as punto says, the chances are smaller.
My read on how to manage a suspected fire in a small recip helo? Do NOT shut down the engine if you THINK there is a fire, just land really fast. Enter auto if you KNOW there is a fire, and then shutdown that engine, close the fuel valve and make a nice landing.
In a transport, you have minutes to diagnose, fix the problem and follow the checklist.