A chainring bolt tool is not really a "special tool". Those chainring nuts with the slot are standard on modern cranks as well, although slowly bring replaced by Allen (thankfully).

Give it a try before trying heat. It might come right off. If it's giving resistance then just let it soak in oil. Eventually you can try heat. Don't use a blowtorch for too long or else the chrome will flake off the bolt. You're way more likely to round out the nut slot than break the bolt here.